I am helping a friend setup an off grid solar system for his vacation home in Baja California.

He came across a deal and now has 70 (yes 70) PRC-12100S batteries. We are curious if these will work decently for a solar battery backup setup. Here are the specs for the batteries;
http://www.powerbattery.com/standbyspeci.html

My concern is that these batteries are designed for UPS systems, not RE systems. They might be able to drop to truly deep cycle, but I just dont think that they are meant to drop their charge on a regular basis.

The other issue I have is that they are 12 volts. I have always tried to adhere to the rule of no greater then 3 parallel strings of batteries in a bank, and if we are going to run a 48 volt system we are talking about 12 batteries, 3 strings, each string being 48 volts with only 91 amp hours. Which is an "ok" system, but not really quite as beefy as we were hoping for.

My recommendation to him has been to sell off these 70 batteries he has, even though they are good quality and sealed, and buy some S-530s or L16HC's and do it right.

I am just looking for people's opinions as to whether I am off my rocker, and that he shodu just setup a bank with 17 parallel strings and run a ~1500 amp hour 48v bank that way.

Thanks in advance.

--Rodger Bright

Hi Rodger,

If these batteries are well matched, you can go with more strings. Also since you are dealing with a vacation house, you will not be getting deep discharges every day. For vacation use, the standby batteries might actually be better since they need less float current. It would be a good idea to have a clamp-on DC ammeter to keep an eye on float current for individual strings.

We were planning on having multiple meters, so that we could monitor the bank. I can see your logic with the lofat charge, but they are talking about possibly spending 2-4 weeks at a time at their vacation house. Meaning that in a month where there is lots of sun (which is very common in Baja) these batteries are going to drop down quite a bit every night for possibly 3 or 4 weeks in a row. Thats what I was really worrying about. If it was just weekends here and there then I woudl have figured these were fine, but using them for a true off-grid scenario for an extended period of time worries me. I just imagine a 30 battery array failing after only a year or so, and then we would need to replace all those batteries, and worse, bring all 30 batteries back, which could be a nightmare, as it is 3 hour drive without roads with a good 4x4 with no flat tires or breakdowns.