Advice on RV Set up & Wiring?

[Carv]

So after weeding through all the fluff Sun King has provided some really good information here on how to actually figure out how much charge & discharge your batteries can take WITHOUT damaging the cells.

hybrid batteries like a Golf Cart battery come into play, or very expensive AGM batteries. They have much lower Internal Resistance, thus can deliver much higher discharge currents and much higher charge currents. Example a Trojan T-105 has an Internal Resistance of .003 Ohm's, and thus two in series would be .006 Ohms. On the charge side heating is the limiting factor and for any Pb battery you want to limit thermal capacity to 0.05 watt per AH. Bet no one here even knows that limit. So if we use a single cell Ri = .001 Ohms and the max thermal charge limit is the square root of [ .05 x 225] / .001 = 106 amps thermal limit.

Now on the discharge side you want to limit the rate to no greater than 5% voltage drop. 5% of 12 volts = .6 volts. So max discharge rate is ,6 volts / .012 Ohms = 50 amps. So for a Trojan T-105 you can charge as high as C/2, and discharge up to C/4 without issues of over heating or performance degradation.

Translated:
Here's how to figure out your max Charge & Discharge rates using a Trojan T105 as an example:
Trojan T105s have an Internal Resistance of .003 Ohm's (.01 per cell), and thus two in series would be .006 Ohms total resistance.

Max Charge:
On the charge side heating is the limiting factor and for any Pb battery you want to limit thermal capacity to 0.05 watt per AH.

So if we use a single cell Ri (resistance) = .001 Ohms and the max thermal charge limit is the square root of [.05 (Thermal capacity Limit) x 225 (Rated Ah)] / .001(single cell resistance) = Max Charge Amps to reach thermal limit.

Trojan T105: Square Root of [.05 x 224] = 11.2 / .001 = Square root of 11,200 / Which = 105.83A Max Charge Amps is Thermal Limit/ AKA Max Charge Rate

To Turn it in to Charge Rating for the T105: (224(Ah) /106(Max charge Amps) = 2.11) or C/2


Max Discharge:
Now on the discharge side you want to limit the rate to no greater than 5% voltage drop.
5% of 12 volts = .6 volts.

So max discharge rate is ,6 volts / .012 Ohms = 50 amps.

To Turn it in to Discharge Rating for the T105: (224(Ah) /50(Max Discharge Amps) = 4.48) or C/4

Without issues of over heating or performance degradation.




My Only Question is where did the .012 Ohms on the discharge side come from?

Thanks

[Sunking]

My Only Question is where did the .012 Ohms on the discharge side come from?

Thx for the catch, my bad, I made an error assuming a 24 volt battery using T-105's. instead of 12 volts which now makes it .006 Ohms and 100 amps on paper but not design. Hang in there. A T-105 battery has a total of .003 Ohms. That means each cell is .001 Ohms and 3 cells in series for a 6 volt battery total .003 Ohms. So two T-105's in series is .006 Ohms. The rest is simple 5th grade math and Ohms Law. Voltage = Current x Resistance, and Current = Voltage / Resistance.

You want to limit voltage sag on a battery to some definable percentage to achieve an operational goal. For batteries somewhere around 2 to 5% loss. Otherwise if you take a lot of current from a battery to say an Inverter, if the voltage SAGS to far, your Inverter trips off line from Under Voltage as designed. You have both battery voltage sag and cable line voltage loss to account for. Otherwise you get nasty surprises like a fully charged battery will not supply power to your Inverter drawing 100 amps. Ideally to be functional you want to limit battery and cable loss to 5% between the 2. 5% of 12 volts is .6 volts total to work with. So use 3% for battery, and 2% for cable. 3% of 12 volts = .36 volts. So now we have two known variables to determine how much current the battery can supply. Again Amps = Voltage / Resistance. So .36 volts / .006 Ohms = 60 amps max discharge rate. So now we have the maximum current of 60 amps to be applied to calculate the size of the wire required to limit voltage loss to 2%. 2% of 12 volts = .24 volts. So now we now again from simple math using Ohms Law Resistance = Voltage / Current. We need to keep the wire loop resistance to .24 volts / 60 amps = .004 Ohms or less. So lets say the one way distance between the Battery Term Post and Inverter is 10 feet and the Fuse is 70 Amps. Go back to the chart above and select conductor.

If you followed all that you came up with a 6 AWG conductor and a 60 amp x 12 volt = 720 watt load is what a pair of Trojan T-105's can handle and expect to operate until the battery is fully discharged utilizing all the power.

[sensij]

Now on the discharge side you want to limit the rate to no greater than 5% voltage drop. 5% of 12 volts = .6 volts. So max discharge rate is ,6 volts / .012 Ohms = 50 amps. So for a Trojan T-105 you can charge as high as C/2, and discharge up to C/4 without issues of over heating or performance degradation.

Max Charge:
On the charge side heating is the limiting factor and for any Pb battery you want to limit thermal capacity to 0.05 watt per AH.

So if we use a single cell Ri (resistance) = .001 Ohms and the max thermal charge limit is the square root of [.05 (Thermal capacity Limit) x 225 (Rated Ah)] / .001(single cell resistance) = Max Charge Amps to reach thermal limit.

Trojan T105: Square Root of [.05 x 224] = 11.2 / .001 = Square root of 11,200 / Which = 105.83A Max Charge Amps is Thermal Limit/ AKA Max Charge Rate

To Turn it in to Charge Rating for the T105: (224(Ah) /106(Max charge Amps) = 2.11) or C/2


Thanks

This is great, in theory. Has Sunking (or anyone following along) ever actually charged T-105RE's routinely at C/2? I've never seen anything in Trojan's documentation to support that high of a charge rate. A quick email to their technical support generates this response:

Trojan Battery Response

Dear sensij:

Thank you for submitting your question regarding Technical - Charger.

Based on your comments below:

I'm hoping for guidance on the maximum safe charge rate for these, let's say at 30% discharged and 25 deg C. I understand they are lower internal resistance and will not build up heat as quickly as standard T-105's, but does that translate into a wider allowable range for charge rate? Thanks, sensij

Below is Trojan Battery's response:

Normal charge rate is 10-13% of the C20 rating. Maximum is 20% of C20 rating. Same as for the T-105.

Maybe they just want to legally CYA, but it surprises me the Sunking is willing to go so far out on a limb.

[Carv]

SunKing, why such a big change now on your discharge calculations?

Originally you stated that 5% was the max voltage drop so with the actual resistance number the calculation would be:
,6 volts / .006 Ohms = 100 amps.

But again you've changed your statement to now say the battery is 3% assumed loss so:
.36 volts / .006 Ohms = 60 amps

As you can see your small adjustment applied at the right place to the ASSUMED number makes a HUGE difference in the allowable result. So if we listen to you, how are we suppose to know what is right and what is wrong because we now have two different statements with a 40A difference of what is "safe"?

As most of this is assumptions and as you can see if you change one little thing by 2% you come up with a completely different answer which in the real world has drastic effects (which I demonstrate below), how is someone who is trying to learn this stuff and figure out "how to do things right"/"safely" suppose to know what to believe and what to dismiss as it seems to change with each post?



So lets apply this to my actual situation, I ran 10 feet of 1/O welding cable (#34 strands) and it's rated at 350A from my two series 6V rated at 214Ah. I'm assuming there would be very little line loss feeding the inverter so that would just leave battery resistance so now it's "safe" to use 3%-3.5% loss calculation on the batteries instead of 5% because I ran such a large positive side lead?

I'm asking this because it affects the "safe" real world operation of the inverter by 500W as it's drawing current from the batteries and wither or not it is or is not "safe". See at a 5% assumed loss wouldn't I be able to pull 100A or 1,200W to the inverter "safely" per the calculations above BUT if we assume a 3% Loss then I can only pull 60A or 720W to the inverter.

Unless I'm missing something, this seems Bass Akwards to me, as the resistance loss drops so does the max allowable/"safe" current draw off the batteries????


Hope you can understand why so many people are confused by your posts which seem to contradict themselves as you go deeper down the rabbit hole especially when you throw in examples that do not apply to the actual referenced situation.




Also if Trojan, AKA the manufacturer's response is correct

Normal charge rate is 10-13% of the C20 rating. Maximum is 20% of C20 rating. Same as for the T-105.

This would mean the manufacturer's recommended charge currant is 22.4A (10%) TO 29.12A (13%) with a MAX of 44.8A (20%).

How come above we're coming up with 105A per your calculations? That's a HUGE 60A difference.

[SunEagle]

Try to read slowly and carefully concerning what SK is saying.

The 5% is the "battery and cable" combined loss with the battery using 3% max and the cable at 2% max. Using the 2% max on the cable allows you to calculate the size and distance you can run a DC wire.

[Wrybread]

I ran 10 feet of 1/O welding cable (#34 strands) and it's rated at 350A from my two series 6V rated at 214Ah.

Sorry if this has been covered, but is there a reason you're not installing your inverter closer to your batteries? You could then relatively light wire (extension chord or whatever) from your inverter to your load.

If its a matter of having easy access to your inverter to turn it on and off, there's remote switches for that.

[sensij]

So lets apply this to my actual situation, I ran 10 feet of 1/O welding cable (#34 strands) and it's rated at 350A from my two series 6V rated at 214Ah. I'm assuming there would be very little line loss feeding the inverter so that would just leave battery resistance so now it's "safe" to use 3%-3.5% loss calculation on the batteries instead of 5% because I ran such a large positive side lead?

Whoa, hold on. 1/0 cable may be rated for up to 350 A in a welding application, but not for continuous duty. Typically that would be 200 A, or somewhat less. The "rating" isn't driving the calculations though, the cross-sectional area and resistance are. 100 A over 10 ft on 1/0 will have a drop of 1.7%, more as the conductor heats up. That would leave 3.3% drop allowed for the battery, per the guideline to target no more than 5% drop so your inverter doesn't cut out. The problem is that 100 A on a 0.006 ohm IR battery = 0.6 V drop, which is 5% all by itself, and gives a total loss of (5 + 1.7 = 6.7... too much). Does that calculation make more sense presented this way?

[Sunking]

This is great, in theory. Has Sunking (or anyone following along) ever actually charged T-105RE's routinely at C/2? I've never seen anything in Trojan's documentation to support that high of a charge rate. A quick email to their technical support generates this response:

Maybe they just want to legally CYA, but it surprises me the Sunking is willing to go so far out on a limb.

Yep Trojan certainly does. It is a THERMAL MASS LIMIT of any FLA battery of .05 Watts per AH of heat dissipation. So on a 225 amp battery the max heat power the battery dissipates is 225 x .05 watts = 11.25 watts of heat per cell on a huge thermal mass of a 22 pound battery cell. So answer this question. If you took say 2.5 gallons of water at room temp (22 pounds) and heated it with 12 watts for 2 hours what happens? Not a damn thing worth worrying about right?

Hell no Trojan does not recommend charging at C/2, but an engineer can design such a system to work withing the thermal limits of a battery. .05 Watts per AH of battery is extremely conservative. Now if you want to talk about Lithium Ion cells the limits is 6-watts per AH which works out to around 20C charge and discharge thermal rates. It is not theory Sensij, it is pure science. My numbers come from IEEE, the group that is in charge for all battery testing and specification protocols. We know WTF we are doing and do not share all that valuable information. You have to be a member and pay for it.

My point is the C/12 to C/8 is a generic rule of thumb that can be safely used on ANY FLA battery. To know what the real limits are you have to know some more information like Thermal Limits which is based on the battery Internal Resistance. If you pump 105 amps through .001 Ohms of resistance generates 11 watts of heat. A 3 cell T-105 works out to .003 Ohms and 33 watts of heat when charged with 105 amps for 2 hours. The battery will still feel cool to touch after 2 hours. Do the math.

[Sunking]

OK Carv lets see if I can make things more clear on achieving your objective. I will start with a story. I just returned from a vacation to South Carolina playing golf in Myrtle Beach and an huge RC event call Joe Nall held at Triple Tree Aerodome near Greenville SC. It is a huge 1-week event were thousand of RC pilots come to compete, show-off, and vendors to make huge sales. It is a massive event and most come in RV's pulling Toy Haulers. I got into the hobby 4 years ago and met a guy named Ron Moore (friends call him Moron, and foe call him Mr. Moore). Moron is a retired FAA director who spent his career maintaining FAA communication facilities power and mechanical systems. Moron is also an excellent artist and metal fabricator. I spent 3 nights with Moron in his RV

About 3 years ago Moron traded in his old RV for a new one and a new Toy Hauler Trailer. He used Solar on his old rig but like most had all kinds of problems and asked me to help out with a design which I gladly voluntered my time for. First thing we did is determine his daily Watt Hour needs and wants. He needed 1 Kwh/Day for necessities, but wanted 3 Kwh/Day so he could have a work shop in his Toy Hauler and all the luzuries of home except Air Conditioning. 3 Kwh a day is a huge task especially for a 12 volt system but doable if you plan it out and work around all the challenges an RV throws at you.

In a stationary system you want 5-day Battery Reserve Capacity as this gives you 3-0days of real autonomy aka 3 cloudy daus before you have to run on a generator. On an RV this is not prac tical nor is it needed because an RV is a part time system. On an RV you need 3-Day Reserve capacity which yeilds 2-days of autonomy before you have to use a genny. So first spec is the battery slection. 3 Kwh per day x 3 days is a 9 Kwh battery. At 12 volts is 9000 wh / 12 volts = 750 AH. His load demand, power tools and microwave demanded a 1500 wat Inverrter that uses 125 amps, so battery selection was based on that need. We searched around to figure out what would fit in the space allowed. We ended up using 4 Concorde PVX AGM batteries model PVX 4050T a 6-volt 400 AH battery in a L16 form factor case. They are brutes of the AGM world and can deliver 300 AMPS until completely exhausted with less than 2% voltage sag. Batteries are done.

The real challeng for RV's is they have two huge challenges no one rarely deals with and something most over look and end up failing or spending a lot more money than nessecary to make it work. Those 2 huge challenges are:

1. Most folks do not park their RV's in a location where they have FULL SUn from Sunrise to Suinset. That is a must for any solar application. Park you rRV in FULL SUN and you roast in summer unless you have shore power or a genny to run HVAC.

2. Panels mounted on the roof compound issue 1. When panels are mounted on the roof facing straight up means you need a lot more panel wattage to generate X amount of Kwh.

Pretty simple fix, use an umbilical cord and panel stands so you can park your RV on the southside a tree line for all day shade and put the panels in Full Sun so they can be oriented dues Solar South and at Optimum Tilt Angle for the time of year. Doing that presents one challenge. How to control Voltage drop and is super easy to work around. Our design was perrfect. We used 5 x 200 wat panels. Normally you cannot use a Prime Number like 5 in series because the Voc exceeds most Charrge Controllers. Not any more, we used a Midnite Solar Classic 200. This allows us to wire all 5 panels in series with an operating voltage of 180 volts and an operating max currrent of 6 amps.

For the umbilical cord we a SO 3-conductor power cord made from 8 AWG at 100 feet. When you use high voltage and low current, all those expensive voltage loss problems go away. At 6 amps and 100 feet voltage loss is less than 3%. On one end of the cable we used Anderson PP15 connectors which are a 15 amp generless connectors. We cut off the MC4 connectors on th epanels and replaced them with PP15 connector, and terminated one end of the Unbilical cord with the Anderson PP15 connectors for th epanels. On the other end of the unbilical cord there are lots of ways to do this buy Moron used a Generator Snout Plug and a Generator Snout Receptacle on the RV. Shear genius design and functionality. Plug-n-Play, Safe and Sane.

The last challeng was the panel stands. We were sitting in Chase Lounge chairs drinking lemonade while deisigning. We Moron was guzzling beer. While thinking I looked at the Chase Lounge chair and it hit me like a ton of bricks. I said look Moron at your damn chair and how the backrest mechanism works. Just a simple channel with slots cut in a rail. Perfect and genius design. Super simple and easy to make. A simple frame that folds up and alows you to tilt th epanels at optimum tilt angle. Ron carries the 5 panels in the RV laying on their edge with frame and a bungy cord to hold them secure to a wall while driving and out of the way. When he gets to a parking site just takes the panels out, stands them up pointing due solar south with optimum panel tilt. Rolls out th eUmbilical cord and Plugs it up. A work of art and design.

The rest is pretty straight forward. The RV already has a Batter Isolator for the House Batteries, Inverter, Shore Power Transfer Switch, 50 Amp Battery Charger, and Inverter. All we did was replace the 1000 watt Inveter-Charger with a 1500 watt - 100 Amp battery charger, and ran AC power wiring and Plug for the Toy Hauler 120 VAC power to run his shop, charge RC plane batteries, and lighting.

As for the electical hardware like battery fuse blocks, and 12-volt distribution we got from Blue Sea which you should be using. You want the Battery Fuse Blocks installed directly on the Battery Term Post, and then run a Feeder cable to a Distribution Block that is equipmed with Fuses for the various loads.

Last point here is back to the Battery Isolator. If Moron is only parked for 1 or 2 days, he does not bother deploying the Solar Panels because they are not needed. As he drives to the site, the batteries are topped off by the engine alternator, and he rarely even uses 3 Kwh per day. So his batteries are good for 2 or 3 days before needing recharged. When he packs up and leaves, his batteries are fully charged up by the time he gets home or the next RV Stop. If he is parked for several days and has a few cloudy days, he fires up the genny which is connected to th eShore Power Plug to recharge the batteries.

All those drawings I showed you come from that design. Us them they will serve you well. Use any of the ideas I just presented to you in great detail and no lip service. I am a professional enginer of 40 years, not a shade tree mechanic. Plan your system out to do what you want, and it will serve you well. Failure to plan is a plan to fail.

Good Luck

SK.

[sensij]

Yep Trojan certainly does. It is a THERMAL MASS LIMIT of any FLA battery of .05 Watts per AH of heat dissipation. So on a 225 amp battery the max heat power the battery dissipates is 225 x .05 watts = 11.25 watts of heat per cell on a huge thermal mass of a 22 pound battery cell. So answer this question. If you took say 2.5 gallons of water at room temp (22 pounds) and heated it with 12 watts for 2 hours what happens? Not a damn thing worth worrying about right?

Hell no Trojan does not recommend charging at C/2, but an engineer can design such a system to work withing the thermal limits of a battery. .05 Watts per AH of battery is extremely conservative. Now if you want to talk about Lithium Ion cells the limits is 6-watts per AH which works out to around 20C charge and discharge thermal rates. It is not theory Sensij, it is pure science. My numbers come from IEEE, the group that is in charge for all battery testing and specification protocols. We know WTF we are doing and do not share all that valuable information. You have to be a member and pay for it.

My point is the C/12 to C/8 is a generic rule of thumb that can be safely used on ANY FLA battery. To know what the real limits are you have to know some more information like Thermal Limits which is based on the battery Internal Resistance. If you pump 105 amps through .001 Ohms of resistance generates 11 watts of heat. A 3 cell T-105 works out to .003 Ohms and 33 watts of heat when charged with 105 amps for 2 hours. The battery will still feel cool to touch after 2 hours. Do the math.

I understand what you are saying. My point is that generally, in the advice we share in this forum, we don't try to tune systems to the point where the difference between success and failure depends on carefully made, precise measurements under very controlled conditions. The OP doesn't know the IR of his batteries. In other threads (maybe a sticky?), you presented an accessible way to estimate it through controlled load testing. Maybe, armed with that number for his specific bank, it would be ok to design around something other than the standard FLA guidelines for charge (and discharge) rate. In the context of this thread, it is all just confusing and noise.

[Sunking]

SunKing, why such a big change now on your discharge calculations?

Read. I made a mistake on the first pass. I used 12-millohms of a 24 volt battery when it should have been 6 milliohms on a 12 volt battery. On the first pass I used 5% which was a misleading mistake I already explained. The 5% is total of both battery and wire to work with. If you allow 3% for the battery voltage sag that works out to a real usable .36 volts / .006 Ohms = 60 amps maximum discharge rate. That leaves you .24 volt allowance for wire loss at 60 amps. 60 amps on a 225 AH battery is C/4 discharge.

Now as for Trojans recommended charge rate of C/10 (10% of C), to C/6 (15% of C) is an across the board of all Trojans FLA battery lines. It is generic like C/8 to C/12 you see me me recommend as a general rule of thumb. Both Trojan and I can sleep at night with those conservative ratings. To know the actual limits you have to know the batteries Internal Resistance and that varies greatly across FLA product line. Here is a great example. Trojan makes a T-105 which is a hybrid battery with a marketing name of Golf Cart, and a True Deep Cycle T-105RE battery. The T-105 has an Ri of .001 Ohms per cell, and the T-105RE has an Ri of .0015 Ohms per cell. That means the T-105 can be charged as high as 105 amps and the T-105RE can be charged as high as 86 Amps. Both batteries are being heated with the same 33 watts of heat. They will not get hot unless the temp of the battery was already 120 degrees to start with.

Pretty simple stuff when you know what is going on and have 40 years experience working with the stuff. Just like a Corvette. Chevy would never recommend you exceed the 70 mph speed limit, despite the fact it can cruise at 120 mph all day long. Called CYA. My point is you can charge the T-105 with more than 30 amps, it is not written in stone. But that does not apply to another manufacture battery of lessor quality and high Internal Resistance. Thus C/8 to C/12 works with any FLA battery of any level of quality. Its a pretend Safe Zone millennials and lawyers like free of thinking and challenges.

[Sunking]

So lets apply this to my actual situation, I ran 10 feet of 1/O welding cable (#34 strands) and it's rated at 350A from my two series 6V rated at 214Ah. I'm assuming there would be very little line loss feeding the inverter so that would just leave battery resistance so now it's "safe" to use 3%-3.5% loss calculation on the batteries instead of 5% because I ran such a large positive side lead?

All I can say is your assumptions and ignorance is costing you a lot of money.

Voltage loss is based on the size of the cable, amps flowing through it, and the length. So lets say you have a 12 volt 1000 watt Inverter and the cable 1-Way distance between the battery is 6 to 10 feet. The Inverter requires a 100 Amp Cable with 100 Amp Fuse. Now use the chart I gave you to select the conductor using the 3% column. What did you come up with?

It had better be 4 AWG. A hell of a lot less expensive and easier to work with.

You are not reading and understanding what you are being told. I will work with you, but you need to read and trust me. Trust Sun Eagle, Mike, Jflorey, and Sensij. We are all experienced professionals. Ignore the 20 year experience shade tree mechanic. SE, Jflorey, Mike, and Sensij may not always agree, but none of us will advise you to do something stupid. Jflorey and myself are PE's, and I have 40 years professional experience. To have PE licensure is about equivalent to a med Doctor Phd. It takes 8 to 10 years of formal education and experience, plus two grueling 8 hour exams 4 years apart to be a licensed PE. To keep it requires 2 CE hours every year and documented projects to keep it.

[Sunking]

I understand what you are saying. My point is that generally, in the advice we share in this forum, we don't try to tune systems to the point where the difference between success and failure depends on carefully made, precise measurements under very controlled conditions. The OP doesn't know the IR of his batteries. In other threads (maybe a sticky?), you presented an accessible way to estimate it through controlled load testing. Maybe, armed with that number for his specific bank, it would be ok to design around something other than the standard FLA guidelines for charge (and discharge) rate. In the context of this thread, it is all just confusing and noise.

Sensij he specifically called out T-105 and questioned the C/6 max charge rate of 30 amps. He can go as high as 105 amps with those specific batteries, and he was worried about 35 amps. I am assuring him he is worried about nothing. 5 more amps will not hurt a dang thing.

Give me specifics, and I give specific answers. Give me generic specs and I give you generic answers. That is the way I roll. Sensij you know me well enough if I see someone trying to do something unsafe, stupid, fakers, pretenders, or wasting money I will nail them to the wall. Some take offense and that is OK with me. As you have learned if they hang in there and listen, they end thinking me for giving them my time and strict attention to detail. If they do not want to listen. let them go somewhere else to learn how to be STUPID. No one here goes to the length and details I will go into if the OP really wants help and wants to learn. That fact is clearly demonstrated on this thread. Most of the rest is lip service.

[sensij]

Sensij he specifically called out T-105 and questioned the C/6 max charge rate of 30 amps. He can go as high as 105 amps with those specific batteries, and he was worried about 35 amps. I am assuring him he is worried about nothing. 5 more amps will not hurt a dang thing.

Give me specifics, and I give specific answers. Give me generic specs and I give you generic answers. That is the way I roll. Sensij you know me well enough if I see someone trying to do something unsafe, stupid, fakers, pretenders, or wasting money I will nail them to the wall. Some take offense and that is OK with me. As you have learned if they hang in there and listen, they end thinking me for giving them my time and strict attention to detail. If they do not want to listen. let them go somewhere else to learn how to be STUPID. No one here goes to the length and details I will go into if the OP really wants help and wants to learn. That fact is clearly demonstrated on this thread. Most of the rest is lip service.

ok! I think you've seen sometimes that the generic answers you provide get applied incorrectly to specific questions, and that leads to confusion. I don't know how to prevent that.

At this level of granularity, I'd like to just caution that all of the resistance based calculations you've presented are a function of temperature. If the battery (and conductors, for that matter) are very hot or very cold, IR, conductor resistance, etc will all move, and maximum charge/discharge rates may need to be adjusted. When moving away from manufacturers' recommendations, the environmental conditions matter. PE's are trained to work in that design space. Folks trying to optimize to that degree will never get there if a forum like this is their only source of information.

[Sunking]

At this level of granularity, I'd like to just caution that all of the resistance based calculations you've presented are a function of temperature. If the battery (and conductors, for that matter) are very hot or very cold, IR, conductor resistance, etc will all move, and maximum charge/discharge rates may need to be adjusted. When moving away from manufacturers' recommendations, the environmental conditions matter. PE's are trained to work in that design space. Folks trying to optimize to that degree will never get there if a forum like this is their only source of information.

Ah but Sensij you are correct but overlooking something very important, Ohms Law and batteries are self regulating. As their Ri goes up means they cannot accept high charge currents even if the charger is capable. Ohm's Law still works. Now if you have a sick and/or severely over discharged battery with low voltage, then yeah you can get into trouble if you have Shorted Cells. More times than not a sick battery has open cells, and a over discharged battery has much higher resistance and thus eliminates the danger. That cold battery does have high resistance but guess what happens as it warms up being charged? A problem for Lithium Ion, so much so you cannot charge or discharge them at freezing or lower. Not a problem for Pb.

I certainly am not recommending you charge FLA's at C/2, far from it. All I am doing is telling Carv is if he is using T-105 don't worry about 5 more amps than the manufactures very conservative recommendation on a 225 AH battery. 30 amps is rough C/7, and 35 amps is roughly C/6. No problem and easy to figure out because Trojan shows both charge and discharge curves at C/5 what a golf cart uses.

If you look at Rolls, they show curves all the way up to C/1. Like this a S-290, a 6 volt golf cart battery, T-105 competitor. Take a look, you are good to 83 amps. If you know how to read the spec you can get Ri at 32 degrees in the MCA spec of 932 amps which means 3.6 volts / 932 amps = .0038 Ohms @ 32 F. You just gotta know what to look for and how the game is played.