Best battery for backup applications

[josepr]

Greetings,

There seems to be two schools of thought about lead acid batteries for backup (float service).

One recommends flooded batteries. Proponents main argument is that if you made a mistake you can equalize them. This argument is unquestionable, is true. That is one of the advantages of flooded batteries. The second one is cost. But it seems that the recommendation is not a generic one. Most authors (tech documents) and proponents (Sunking) usually recommends them for float service only if they are lead-calcium. Those type (flooded) are not commonly available for off grid use. They are mainly used by the telecom industry. What most of us can get are lead-antimony (RE: L16 and Golf cart, etc.) It seems that most manufacturers do not recommend them (although one manufacturer says that you can use them but at least deep discharge them once a month {source: web seminar}). Mainly because of stratification and lost of capacity in float service (although, according to one manufacturer you can recover the capacity if you cycle them).

The other school recommends AGMs. Mainly because they are maintenance free (but you should check and retorque connections 2 times a year). The second reason is that, because the electrolyte is captive, the do not suffer from stratification. The third one is that most of them are lead-calcium (like to float). The disadvantage is that lead-calcium has less cycle life than lead-antimony. Another point in favor is that in most backup applications the battery is going to die because of age, not because of end of cycle life.

Personally, I’m more into AGMs, for backup (float service) because, as several pro installers have told me, people (grid tied) tend to forget they have batteries that they have to maintain. This happened to me with two golf cart batteries. Left them on the charger and 4 months later remembered them. Fortunately, the plates were still (barely) covered.

So, my question is: Do you think that, even with its disadvantages (stratification & lost of capacity) that flooded lead-antimony batteries are worth it in backup applications? If you have flooded lead-antimony in float (backup) service, please let us know what your experience with them has been. Thank you.

[Mike90250]

Don't forget cost per watt delivered
12V 200ah from 2 GC2 flooded batteries = $200
AGM version = $ 360 and shorter life.

My recommendation:
Get Flooded batteries for your first set. You NEED to remember to look after your system, inspect it weekly at least. If you make a mistake, no problem, they were cheaper batteries anyway. Basic golf cart batteries should last you at least 3 years, if sized properly.
Once you have a set of batteries that lasts, or you know you have solved all your problems, then spend the extra $ ( nearly twice the cost, for about half the lifetime ) for AGM batteries.

Remember nearly 80% of batteries die from insufficient recharging, the rest from old age. Over charging with solar is too rare to mention.

Study the cycle life and depth of discharge graphs for your chosen batteries before you purchase.

[josepr]

I’m still not sure if I should use flooded lead-acid (Lead-Calcium) or an AGM for backup applications. The batteries will see action 5 to 10 times a year for 1 to 6 hours. But during an emergency could be cycle every day for months. Last hurricane we go without power for around 2.5 months. An we were the lucky ones. Some areas went without power for 1 year.
I like the idea of being able to check the state of charge (hydrometer) and adjust charge parameters (during an emergency). The only problem is that the only ones available where I live are telecom batteries (expensive). It seems that they are not produced (the flooded version) by the leading manufacturers (Trojan, Rolls & Crown). If you want to buy lead-calcium from them, you are limited to AGMs.

Other option I have been exploring is using lithium. The only problem is that I found, what seems to be a doctoral thesis, about the rapid deterioration of lithium cells when exposed to float charging. I do not remember the chemistry. Maybe that does not apply to LiFePO4. The majority of the drop-in replacement manufacturers do not recommend float charging. That’s ok. Inverters & solar CC can be configured to not float charge. But there seems to be another problem. Some experts do not recommend keeping lithium cell at 100% for a long time. They recommend keeping then at 70% or 60%. That would make lithium like 2 to 3 more times expensive compared to a lithium bank for cycle service. That would be like 4 to 6 times more expensive that lead-acid for backup (float) service {for cycle its 2 to 3 times more expensive}. Because that implies a bigger battery bank. Is that correct? Thank you very much.

[Sunking]

But it seems that the recommendation is not a generic one. Most authors (tech documents) and proponents (Sunking) usually recommends them for float service only if they are lead-calcium.

Afraid you might have misunderstood. True Telecom and others that use batteries in Float Service do use Lead Calcium because they have lower self discharge rates and longer Float Service life than Lead Antimony. They do not cycle them. Lead Calcium if cycled only have 50 to 200 cycles in them. However in Float Service will last 20 years. Even better is pure lead with a service life of 30+ years and still counting.

AGM's are also use din Telecom for niche applications. Most notable in tight confined spaces where gassing cannot be tolerated if over charged and prone to thermal runaway. But make no mistake about it, AGM do not have the Calendar or Cycle life of FLA.

You got most of it right about Lithium, they do not last as long as Pb, an din the end 4 to 10 times more expensive. What you got wrong is Lithium can be floated like any battery. Actulaay extremely easy to do. You are on the right track, never ever charge Lithium to 100%, 90% is more than enough. We use some Lithium in Telecom and we do nothing special fo rthem. They use the same battery plants, and exact same voltages as Pb. We float them @ 54 Volts 24 x 7 x 365. We restrict their use to Micro Cell Sites like a Wllamart, Stadiums where we only need 1 or 2 hours backup at a high discharge rate. Otherwise we have no use for them.

[josepr]

Afraid you might have misunderstood. True Telecom and others that use batteries in Float Service do use Lead Calcium because they have lower self discharge rates and longer Float Service life than Lead Antimony. They do not cycle them. Lead Calcium if cycled only have 50 to 200 cycles in them. However in Float Service will last 20 years. Even better is pure lead with a service life of 30+ years and still counting.

Yes, I misunderstood.

Honestly, I do not now what to do. I must choose the chemistry of the batteries for an AC couple Inverter, used for backup (critical loads). Originally intended to use AGMs, mainly because that’s the norm these days. But was seriously considering using industrial flooded lead-antimony (Trojan Solar Industrial Line or Rolls Series 5000). But because of recent developments (lead acid with silicon wafer and new lithium chemistries), in addition to the price deflation trend of LiFePO4 batteries. Maybe I should wait, buy standard run of the mill batteries (L16s) and wait it out for 3 to 4 years.

PS: Thank you for your time and dedication. Your posts and answers are invaluable. Again, thank you very much.

[Sunking]

But was seriously considering using industrial flooded lead-antimony (Trojan Solar Industrial Line or Rolls Series 5000)

Sir you cannot possible go wrong with either battery. Buy a Lithium and you get a 1-year warranty and a 3 year battery. Buy a Trojan Industrial Series and you get a 36/120 warranty. That is full replacement for the first 3 years, and prorated for the next 7 years at half the cost of Lithium. No one offers that kind of battery warranty because no one makes that good of a battery. Rolls 5000 series is the next best with 7 years.