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I just installed a 48 V ebike conversion kit on one of my bicycles. I will power it with 4 12 V, 12 Ah, lead acid batteries connected in series because of the cost of 48 V, 12 Ah lithium batteries designed for the purpose. (I may buy the lithium batteries later if I find that I use the bike regularly.)

My question is in regards to charging the batteries. It seems that I have three choices:

1) Charge each battery individually with a 12 V charger.

2) Charge them in parallel with one 12 V charger.

3) Charge them in series with a 48 V charger.

I currently own two 12 V chargers and no 48 V chargers. I am thinking that charging them in two banks of two, in parallel, would be my best option without buying more chargers. Any comments on the pros and cons of any of these options would be appreciated.

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    \$\begingroup\$ Ideal would be four 12 V chargers, each of them with floating secondary. That way you don't need to worry about balance charge then either. \$\endgroup\$ – winny Jul 25 '17 at 21:59
  • \$\begingroup\$ see also electronics.stackexchange.com/questions/14174/… \$\endgroup\$ – Jonas Stein Jan 10 '18 at 23:38
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You can charge them in parallel, assuming your charger has sufficient current capacity. The charger will be effectively charging a 48 Ah battery. That should be in range for a normal off the shelf car battery charger.

Even if the charger's current capability is lower than what the batteries could be charged at, as long as it can sustain the float charge current, the batteries will eventually get charged. Since the float charge current is rather low, pretty much any "car battery charger" should be able to eventually charge these batteries.

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