those chargers should have a circuit breaker on the panel, make sure that is not tripped.
as far as charging? you can go lower than 50%, by design you can run it down to the low end of the charge and everything should still work just fine. I just wouldn't run them completely down till it doesn't want to move. I would wait till the BDI gets down to about 3/4 discharged before putting them on charge.
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