| Ian,
what are you charging the batteries with? How many amps is your battery charger rated at?
You may be using to big a charger (too many amps), or charging the battery too long, (or both)!
The fizzing you hear is the electrolyte boiling (gas bubbles) venting.
Was the battery warm to the touch after be on charge for 5 hours?
You do not want to overcharge & boil off your electrolyte on a sealed lead acid battery. While I am sure no harm was done, you may want to fine tune your battery charging to get the most longevity out of your batteries!
Steve C. |