Comparing Lead Acid battery bank vs. AGM

jcpers

I have a 48 volt battery bank of Trojan L16E 6 volt lead acid batteries connected in series.  On the Trojan website, each battery is rated at 340 Ah @ 10 Hr.  The bank is 4.5 years old, where two of the batteries recently died (reading 4.2 v without a charge).  It is my understanding that I need to replace all 8 batteries.

A solar company recommended that I replace these with AGM batteries with four NorthStar Blue+ 12v 210Ah.  On the NorthStar website https://www.northstarbattery.com/product/nsb-210ft-blue these batteries are rated 10 hr capacity to 1.80PVC at 200 Hr.

My question;  I want to know whether or not I am increasing or decreasing my storage capacity by replacing current battery bank, the six Trojans 6v batteries, with four NorthStars 12v batteries.  I am not very battery savvy and really appreciate any help.

Thanks

mike95490

The old ones are 6v 340Ah  x 8 =  48V @ 340ah
New ones are  12v 210ah x 4 = 48v 210ah    so they are quite a bit smaller, and are going to be pretty expensive.  If you have no special need for sealed batteries, which I think, don't last as long as flooded.   Why not replace with the same L16 as you had ?

jcpers

Mike, thanks for your response.  If I understand you, I would need two sets (four 12v batteries each) of the NorthStar AGMs to have around the same storage capacity of the eight lead acid Trojans.  From the quotes I have received on both battery types, it would be around $2,000 for the eight Trojans and $4,600 for 12 NorthStars to achieve around the same storage capacity.  I don't have a special need for sealed batteries but was under the impression they last longer.  My battery bank is subject to ambient temps with the occasional low below 0 degrees F.  And, the occasional high around 100 degrees, mostly 22 - 90 degrees.  I live in Southern Missouri.

mike95490

Yep, pretty much what I intended to say.   With some folks that cant be bothered to maintain flooded, sealed last longer.

Estragon

At 4.5yrs, the flooded may have died a bit young, but you must have been doing at least some maintenance for them to last that long? 

Would you get over 2x the life from AGMs for the over 2x the $$?  Unlikely IMHO.  Is it worth $2600 to avoid periodic watering and SG checks?  Only you can answer that.  For me, being able to measure SG is a feature not a bug, but not everyone sees it that way.

jcpers

Estragon, I measured voltage monthly and added distilled water as needed.  I did not know about SG checks.  If SG checks are off, what does one do to rectify?  The Batteries are connected to a Xantrex  XW MPPT 80 600 Solar Charge Controller & a Xantrex XW Series Hybrid Inverter/Charger where the system cuts the load at 50% charge.  Based on the comments above, I am leaning towards the Flooded Lead Acid, but want to be sure I am maintaining them properly.  Any help would be appreciated.

Estragon

I spot check (couple of cells) water ~ monthly, and full SG & water (all cells) ~ quarterly.

If SGs are off (eg some at 1.28, some at 1.25), I do equalization cycle(s), which is basically a controlled overcharge. Depending on bank temp, it's done at ~16v and continues until the lowest cell or two stop rising.  The batteries gas more in EQ, so you need to keep an eye on water levels in the process.  Some do this on a regular schedule (eg monthly), but it's hard on the stronger cells so I prefer to do it only as required.  Depending on available sun, it sometimes has to be done over a couple days.

The hope is to have weaker and stronger cells all age at about the same rate and not have a couple weak ones require a whole bank replacement prematurely.

The same thing can happen to AGMs, but with no ability to check SG it's difficult to impossible to catch, and with limited ability to EQ (too high voltage can permanently damage AGMs), difficult to remedy anyway.

Surfpath

Hi, I have had a L16RE-B bank for 6.2 years. A few months ago I had one cell die on one of the batts (it always had slightly high SG's), and replaced that batt with 2 golf cart batteries. Generally I think I have been good to my bank (averaging 65-75% SOC minimums/day). Average bank temp is ~80-84 degrees (f). Perhaps my only issue was slightly too long absorbs for a few years. I hope my current set up will last another 6 months or so. I think you can get 6-7 years out of the RE's if you monitor them fairly periodically (make sure to learn how to take an SG, it's pretty easy). I am pretty sure I will re-bank with another Trojan product (perhaps one of the SPRE's, heavier, potentially longer lasting 6V's).

Surfpath

I meant one of the Trojan SIND's, not the SPRE's (which is Trojan's new name for the L16RE line):

https://www.trojanbattery.com/pdf/datasheets/SIND_06_610_DS.pdf