Battery Charging Question

[ScubaLatt]

I have a 24 V troll motor. My question is related to how best to charge the batteries. I could buy an on board charger that I hook up "permanently" to the batteries and just plug it in. But, I already have 2 small 12 v chargers. Question is: Can I hook the 2 small chargers to seperate batteries at the same time and charge them that way or do I have to disconnect them from series to properly charge them?

Any other suggestions are welcomed.

Thanks!