http://www.rv.net/forum/index.cfm/fuseaction/thread/tid/23331296.cfm(QUOTES FROM THE ABOVE LINK):
"Hi,
WHEN YOU ARE GOING TO DO A REALLY HIGH VOLTAGE CHARGE, IT IS BEST TO REMOVE THE CAPS TO NOT OVER PRESSURIZE THE BATTERY. There is a lot of hydrogen going out of the battery when you get it up to 14.4 volts for a equalize charge. It will also allow a little more heat out of the battery.
When at a normal charge rate of 13.2 or 13.5, it is not a requirement to remove the caps from normal batteries.
I equalize the battery about every 3 months. It insures the battery does not get a hard build-up of sulfur on the battery plates, and makes sure everything will last a long time.
Good luck,
Fred"
"The information probably came from the "product liability" legal section of the company. IF THE CAPS ARE OFF THERE CAN'T BE A BUILD UP OF HYDROGEN TO EXPLODE and they have no chance of a law suit. It's not likely that any maintenance style charger when operating properly could ever build up pressure greater than the vents could handle but it JUST MIGHT BE POSSIBLE FOR THE CHARGER TO NOT WORK PROPERLY AND/OR THE VENTS BECOME CLOGGED BY SOME MEANS. If these unlikely thing should occur the company doesn't want any liability."
"worked in an exide battery plant here back in the mid 90S....HAD A FEW EXPLODE WHILE BEING CHARGED....ya don't wanna be in the same room with em when they do.
they don't put the caps on em when they initialy charge them at the factory, for whatever that is worth....of course they dump the acid out and refill em with a different specific gravety acid for the final shipment to the stores.
steve"
As the above link provided by Routy indicates, batteries can swell or explode, if venting is insufficient or the charger malfunctions. Thats why you remove the caps when charging, in a well ventilated area with no flame or spark present.
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