Battery charger question
 

Have an on board trickle charger boiling the water out of batteries. Bad charger?

if the batteries are charged and it wont shut off then yes the charger is bad but if its a bad battery that wont take a full charge then the charger may be working fine.

is it just one battery being boiled or both? if both then I would be thinking a bad charger, if it is just one battery doing it then I think its more likely its that battery has issues but switch the leads around on the charger to see if its just one bank on the charger that is stuck on full charge

Thanks for the reply. Both batteries have boiled out. One faster than the other.
Can I go back with water only or do I need to add battery acid. Both batteries less than six months old.

add distilled water

sounds like the charger needs to be fixed or replaced, it might be a cheap fix if its worth it depending on brand and quality