Vent Caps on Batteries - on or off when charging

[kampingkoge]

I bought a new 3 stage "smart charger" last night.  Owners manual says to check the batteries owners manual as to whether or not to remove the vent caps during charging.  I have 2 batteries, both have removable vent caps, a marine starting and a marine/rv deep cycle.   No owners manuals, what are the battery experts opionion on this.

Thanks in advance.

[AustinBoston]

I bought a new 3 stage "smart charger" last night.  Owners manual says to check the batteries owners manual as to whether or not to remove the vent caps during charging.  I have 2 batteries, both have removable vent caps, a marine starting and a marine/rv deep cycle.   No owners manuals, what are the battery experts opionion on this.

Thanks in advance.

I would leave the caps on during normal charging, but remove them during a "conditioning," "equalizing," "antisulfation," or a "bubbling" cycle (I think those are all the same thing, but I'm not sure).

I'm expecting someone to correct this if it's wrong...

Austin

[wavery]

The biggest problem with battery charging is that the chemical process produces an explosive gas.

In most cases, this gas is not a problem if the battery caps are vented (most are). The idea of removing the battery caps is to defuse the explosive gases by dispersing the gases into the air. Leaving the caps on has the potential of the gases accumulating so densely that it can become dangerous when exposed to an ignition source. The battery in your car is being charged every day, with the caps on. However, the charging is controlled and there is no ignition source close enough to reach the gases inside the battery.

When you are "conditioning," "equalizing," "antisulfation," or  "bubbling" the battery gets hot and the gases increase greatly. That's when it becomes particularly important to defuse those gases as AustinBoston stated.

Personally, I always remove the caps when charging my camper battery. I saw a battery explode once. It's not pretty.

The dangerous part of battery charging is disconnecting the cables when removing the battery charger. If there is a spark and the density of gas is high enough (not very common) you could have an explosion with hot battery acid dowsing everything in sight.

[AustinBoston]

The dangerous part of battery charging is disconnecting the cables when removing the battery charger. If there is a spark and the density of gas is high enough (not very common) you could have an explosion with hot battery acid dowsing everything in sight.

Most of this risk can be avoided (but not all - it depends on the charger) by making sure the charger is off and unplugged before disconnecting the battery.  

The problem is, it's kind of instinctive to disconnect the battery first.  Even knowing this rule, there have been times I've caught myself when the clip sparked...oops, did it again.

Austin

[dthurk]

How about using a pigtail from the negative battery terminal to the battery charger clip?  Helps keep the spark away from the battery.

[wynot]

I remove my caps when charging with a battery charger, simply because it charges heavily at high current, lower volts when starting and progressively reduces current, increases voltage as it charges.
 
I put a rag over the openings so that the bubbling doesn't hit everything.