12v batteries in series

Does it matter which combination of pos/neg posts I attach my battery charger to in a two 12v battery in series configuration? (I assume a neg off one and a pos off the other) Also in relation to this, does it matter which posts are used as my outgoing power lead hook up? In other words, would it be a problem to use the same positive post as my hookup point for outgoing power and charging as long as I wasn't charging while running anything off the batteries? I hope this makes sense and thanks.

I have a bass boat that is 36v I just attach charger to first battery in the series.To charge them allMy wife thinks bagging a truck means you kick it in the truck nuts

Thanks man!