I'm a bit late posting about this, but last year I had quite a problem.
A little history: When I started building my house about 8 years ago, one of the things I soon did was set up the battery bank and inverter system. I was tired of having to run a loud noisy generator all the time to run power tools. It was nice and quiet, except when I needed to charge the batteries. At the time, I didn't know a whole lot about FLAs, and we would run them down until the LBCV on the inverter would cut in, and then charge them back up. Pretty heavy abuse of batteries, I now know. Finally, the house was finished, and I had a kind of crude battery box outside the shop door on a concrete slab. The first winter we had some pretty cold times (-20F and stuff) and I noticed the battery capacity was really going down when the cold would hit. More LBCV action, starting up the generator at 4 in the morning, that kind of stuff. More battery abuse, eh?
The next spring I built some home-made SIP panels and moved the batteries into their nice insulated container in the basement with a fan to the outside that was hooked up to a relay off the AUX pin on the MX60 charge controller to vent when charging. Things now worked well for several years. After 7+ years, though, I could tell these badly abused batteries were starting to be on their last legs: charging efficiency was down, and they were taking more water than they used to, etc.
Well, now for the drama! Luckily I was home. I noticed that the dishwasher turned off before it should (yes, my wife really likes a dishwasher!). I went in the kitchen and turned it back on. It worked for about 10 seconds, then turned back off. What? I ran downstairs and the battery box was emitting thick black smoke and was starting to get on fire! I immediately donned a good respirator that I had, grabbed some dykes, flung open the door, turned off the power to the inverters, and opened the box and started cutting battery cables. I hauled them all outside and started airing out the building. I'm now without power, but the house didn't burn down.
I had (now have new) 16 L16 batteries, arranged in 2 parallel strands containing 8 on each strand for a 48 volt system. What I have since learned is that it is a VERY good practice to have a nice hefty fuse (say 100A or 150A) on one of the connections between the two parallel strands. What happened in my case is that one of these poor old batteries developed an internal short, and when that happened, the other parallel bank started to dump ALL of its power into that shorted battery. The results were almost catastrophic.
I've been told in a recent workshop that about 1 in 10 RE installers know about fusing the parallel strands and do it, but many (including this DIYer) do not. If you have parallel strands of batteries and have not done so yet, hop to it! You've been warned!
All the best,
Tim
