Walmart Everstart marine deep cycle batteries can't handle high current discharge?

[william2021]

Hi, I'm new to solar so please tell me if I made any stupid mistakes. I bought two EverStart Maxx Marine Batteries, Group Size 29DC (12 Volts) from Walmart (https://www.walmart.com/ip/EverStart...5-CCA/20531539). They are rated at 122 AH.

They are connected in parallel to Renogy 2000W pure sine wave inverter. I thought that should be able to power 600W equipment for say one hour without problem.

However, when the batteries started at 12.85V, upon producing that 600W, the voltage steadily drops quickly, and in a few minutes it's below 12.2V, and even into 11.8V when I stopped it. After that it would return to about 12.5V.

Did I make any mistake?

I later learned that Everstart battery is rated for 122 AH @ 1 amp. And some people online appear to suggest it's much smaller at high current discharge. Is that true? I can't find that specs for this battery.

If I switch to Sam's Club's golf cart batteries, will it better? Does this page say it will last 105 minutes when discharging at 75 amp ?

https://www.samsclub.com/p/duracell-golf-car-battery-group-size-gc2/prod3590228?xid=plp_product_1

Thanks so much for your kind help!

William

[SunEagle]

Hello william2021 and welcome to Solar Panel Talk

I see a few things you may not have thought of.

First that EverStart battery is not really a deep cycle type and may not provide anything close to the 122 Ah rating you mention.
Second is that Renogy 2000w inverter will consume at least 100watts per hour while turned on, so tack the amount onto your load wattage.
Next do you really know what your load is? Have you used a kill a watt meter to measure what it really consumes in watt hours?
Finally before you spend any more money on batteries first know what you are consuming in watt hours per day (including the inverter). You really want to get a deep cycle battery that can provide you about 25% DOD each day and still have a lot of cycles for it's lifetime. If you go with a cheap battery you run the risk of killing it quickly and needing to replace it often,

[william2021]

Hi SunEagle, thanks so much for your kind help.

Indeed I later searched on the forum and someone else mentioned another problem with these batteries, ie they won't yield the perceived capacity: https://www.solarpaneltalk.com/forum...ttery-capacity

So I will try to change to the Sam's Club's golf cart batteries mentioned above soon and see what happens. That is a true deep cycle battery and, its webpage above says it will last 105 minutes when discharging at 75 amp, is my understanding correct?

That Renogy 2000w 12V inverter has No Load Current Draw: < 2A, as in https://www.renogy.com/2000w-12v-pur...wave-inverter/ . That means it consumes <24watts per hour while turned on, right?

I have a SmartThings Wifi Smart Plug, that shows power consumption through wifi to my smartphone, so I can easily see power running through it in real time and historic data. I think it's similar to kill a watt meter as you mentioned.

Yeah many people online praised this Walmart Everstart marine deep cycle batteries for solar, but now I realize / recalled that they may either bank many such batteries (>7) so can power large appliances, or having only a couple such batteries but only power low watts. In my experience, two such batteries is about capable to power 300watt continuously, but would struggle beyond that wattage.

That is, if I didn't make mistake somewhere. I do connect the inverter to the appliances through a 50ft 16AWG extension cord rated at 13amp, not sure if that added problem here.

[SunEagle]

Hi SunEagle, thanks so much for your kind help.

Indeed I later searched on the forum and someone else mentioned another problem with these batteries, ie they won't yield the perceived capacity: https://www.solarpaneltalk.com/forum...ttery-capacity

So I will try to change to the Sam's Club's golf cart batteries mentioned above soon and see what happens. That is a true deep cycle battery and, its webpage above says it will last 105 minutes when discharging at 75 amp, is my understanding correct?

That Renogy 2000w 12V inverter has No Load Current Draw: < 2A, as in https://www.renogy.com/2000w-12v-pur...wave-inverter/ . That means it consumes <24watts per hour while turned on, right?

I have a SmartThings Wifi Smart Plug, that shows power consumption through wifi to my smartphone, so I can easily see power running through it in real time and historic data. I think it's similar to kill a watt meter as you mentioned.

Yeah many people online praised this Walmart Everstart marine deep cycle batteries for solar, but now I realize / recalled that they may either bank many such batteries (>7) so can power large appliances, or having only a couple such batteries but only power low watts. In my experience, two such batteries is about capable to power 300watt continuously, but would struggle beyond that wattage.

That is, if I didn't make mistake somewhere. I do connect the inverter to the appliances through a 50ft 16AWG extension cord rated at 13amp, not sure if that added problem here.

I am not sure if those Sam's Club batteries are good for solar but when looking for a battery you should have the Ah rating based on 20 hours. If the time is less than 20 hours the Ah rating is higher and misleading.

As for the inverter. You are correct it will consume < 2A but if you use the output voltage that calculates to over 200watts (2A x 115V = 230watts) so add that to your load to determine watt hours consumed.

And last data point is the wire size between the inverter and battery system. A 2000w 12 volt system can draw 167amps or more depending on what the load is. So your wires need to be sized to handle about 200amps and have fusing that protects it.

[william2021]

Thanks. That Sam's Club page did specify that battery as:

20 amp hour rate:215
5 amp hour rate:157
6 amp hour rate:156
Battery Electrolyte Composition:Acid
Minutes at 25 amps:395
Minutes at 75 amps:105
Volts:6

So if I understand it correct, that means:

at 20 amp, it discharges for a bit more than 10 hours (215/20)
at 5 amp, it discharges for 31 hours (157/5)
at 6 amp, it discharges for 26 hours (156/6)

at 25 amp, it discharges for 395 minutes
at 65 amp, it discharges for 105 minutes

Is that correct?

As for the inverter. You are correct it will consume < 2A but if you use the output voltage that calculates to over 200watts (2A x 115V = 230watts) so add that to your load to determine watt hours consumed.

I'm confused by this. When I saw that 12 volt based inverter powers 600W appliance, the current was 600W / 12V = 50A, right? Then by the same token, a 2A draw is always 2A * 12V = 24W, right?

[william2021]

Thanks for mentioning the wire size. I guess it works like this, the circuit between the battery and the inverter is 12V, while the circuit between the inverter and the appliance is 110V. That 2000W circuit is the latter, so it's 18A maximum, and 600W is less than 6A. Hopefully I will get that Sam's Club's golf car battery soon, and will let you know how it works, and I will definitely try directly hooking up the appliance if needed.

Thank you so much! as I believe I learned how to interpret those number now. (I still don't understand why they mention both "20 amp hour rate" and "Minutes at 25 amps" and whether they are different though, hope that doesn't matter much.)

[SunEagle]

Thanks. That Sam's Club page did specify that battery as:

20 amp hour rate:215
5 amp hour rate:157
6 amp hour rate:156
Battery Electrolyte Composition:Acid
Minutes at 25 amps:395
Minutes at 75 amps:105
Volts:6

So if I understand it correct, that means:

at 20 amp, it discharges for a bit more than 10 hours (215/20)
at 5 amp, it discharges for 31 hours (157/5)
at 6 amp, it discharges for 26 hours (156/6)

at 25 amp, it discharges for 395 minutes
at 65 amp, it discharges for 105 minutes

Is that correct?


I'm confused by this. When I saw that 12 volt based inverter powers 600W appliance, the current was 600W / 12V = 50A, right? Then by the same token, a 2A draw is always 2A * 12V = 24W, right?

If you are sizing the wire on the inverter output you divide the load wattage by the output voltage. (600w / 115v = 5.2 amps). Sizing the wire between the battery and inverter you divide the inverter wattage by the battery voltage (2000w / 12v = 167amps).

So I may be wrong but to get a better estimate of how may watt hours you consume it would be smart to multiply the inverter usage amp rating (<2A) by the same voltage of 115V which calculates to over 200watts.

[william2021]

Hi SunEagle, thanks so much for your kind help. I bought two Duracell 6V golf cart batteries as mentioned above and connected them serially, but got the same result. That is, upon applying 600W load, the battery voltage quickly drops from 12.6V to 11.8V. And after turning off the load, the battery voltage quickly returns to 12.5V.

I changed the inverter to Renogy's 1000W one, whose no-load amp draw is half, at 1A. I also directly connect that 600W appliance to the inverter. The power cords from the batteries to the inverter are 2AWG.

What do you think I could get wrong?

Thanks so much!
William

[Mike90250]

A 600w load @ 12V is 50A, quite a lot for a 200ah battery to handle (actually, closer to 60A when conversion losses are added in)

You need to study Peukert's law about high discharges on batteries https://en.wikipedia.org/wiki/Peukert's_law

what you experience is not unexpected.

[william2021]

Hi Mike90250, thanks so much, that explained spot on, as that wiki page of Peuker's law said that countrary to the apparent reading, the energy is actually still there, that's why the battery voltage would return after removing the load.

Someone else also asked the same question here: https://diysolarforum.com/threads/vo...er-load.10744/ . So in conclusion:

1. voltage drop to below 50% during heavy load is expected, according to Peukert's Law.
2. that wiki page did not say this would cause long term negative effect on the battery.
3. it could also be fueled by too thin wire.
4. this effect can be lessened by adding more batteries.

Thank you all so much! This issue is resolved and I learned so much new from you!

Best,
William

[Mike90250]

What you have to watch for, is internal heating of the battery with heavy loads or charging. That excessive heating warps plates and eventually causes shorts internally

[william2021]

Hi Mike90250, thanks for the reminder. I have a Sunnyskyp 60A MPTT charger, but indeed I forgot to tape its temperature sensor to the new battery. I just taped it, will that watch for the temperature during charging automatically?

I forgot to mention that in the other post I linked above, someone also suggested that, while the voltage drops during heavy load, we can also just watch closely the voltage, if it will remain steadily around 11.9V, that might also be fine. Or they said as another youtuber mentioned, we may just set the voltage alarm to 11.5V during such heavy load situation.