The dumb chargers got them up to 10v or so... but then they started to balloon. They died. I'll have to run with my 9ah motorcycle battery until I get paid and buy a couple of 2100mah 3s batteries to link in parellel. 4200mah is more than twice what I had will easily last 8 hours... and its a lot lighter and smaller than the motorcycle battery thats filling my rear cargo box!