The primary question is what is the voltage of your battery
charger when the cell is bubbling? If it is over 15 volts DC then there is something seriously wrong with your battery
charger.
- - If the voltage is less than 14.5 volts and only one cell is bubbling there is something wrong with the battery. All the cells in any one battery should react the same during
charging. If one is bubbling and the others are not then you have a bad cell in that battery.
- - The majority of problems occur because of improper battery
charging. You need to know the voltage during the charging and the amperes going into the
batteries. Using a automotive battery charger on
marine batteries is not good for battery life. Use a "smart charger"
designer for
marine batteries. Invest in a digital volt meter and digital ampere meter to
monitor what is happening to your batteries.
- - Here is a good Q&A on batteries:
Deep Cycle Battery FAQ
There are many other similar sites on-line to get you up to speed on battery care for your marine batteries.