batteries

Bateries tear loose. When in rough water I am having trouble with my batteries tearing loose. I have had to resecure using larger screws each time and this has happened at least three times in the 3 years I have owned this boat. It appears the deckingmaterial used is plywood underneath...

Thinking about purchasing an Inverter Generator (2000w) to charge boat batteries when electric outlet not available. I have a 3 bank 10 amp charger on board. Will this work? If not, any recommendations would be appreciated. Thanks for help.