I also made a charger for the bank. I didn't like hooking a 12 volt charger to each battery one at a time. Takes forever and the charging isn't equal. I built a charger out of a dimmer switch and rectifiers out of an old alternator. I hooked a cheap digital multimeter up to it for reading battery voltage and amps for charging. In these pics, the battery bank is at 40 volts and my charging current is 1.02 amps. As the voltage rises, the amps fall. When it gets down to about .15 amps it shuts off. I can also leave it on and as I am welding the amps jump up to 3-5 amps or so and drop back down once I stop welding. For a 36 volt battery bank, I can push about 60 volts into it at about 10 amps or so. The dimmer only handles 600watts and at 120 volts, that is 5 amps. I tested it on just 12v and could get about 20 volts and 25 amps or so. I had to use a different meter though...that one is limited to 10 amps.

 

So, this charger is no frills but it gives you a lot of control. Imagine having some batteries that you are going to repair and desulfate. Lets say what I'll have in the near future. I'll have 2x12 volts, 2x24 volts, and a 36 volt. If I jumpered these in series, then that would be 96 volts. I could hook this homemade charger up to each end and turn up the knob. When I hit the bank voltage it will start charging. So all the batteries would be trickle charged and equalized once a month if I like. I could then put the 12 volt desulfator on any 12 volt section I like. Otherwise, by the time I fix one battery, the others would be in far worse condition from just sitting there. Or, I would have to buy 9 seperate chargers. I've seen 25 amp 12volt golf cart battery chargers on ebay for $200. I've seen 12 amp 36 vot golf cart battery chargers for about the same. Mine does that with total control and only cost me $5 for the dimmer switch, $14 for the meter, and the rectifiers were free out of a junk alternator. I think I'll get some cheap digital amp and volt gauges on ebay and put it all in a nice box. We'll see :)