Battery vents for sealed batteries

[alisdair4]

I've just replaced the conventional (wet) batteries on my boat with 2 sealed gel batteries. (2 x 125 AH sealed calcium). Two thirds the size, giving 20% more capacity - marvellous!
The batteries come with no instructions, apart from a label telling you to remove the bung over what I presume is the vent to release pressure when the batteries are charging.

The batteries are here for reference: http://www.performanceleisure.co.uk/dc_range/

The question is, should I be venting these bungs anywhere - eg, into the bilge. With my previous installation, I never did, and there was always a bit of a concern that there would be an accumulation of Hydrogen in the battery compartment - although I presume the gas would eventually escape upwards. Or am I worrying about nothing..?

 

[pvb]

I've just replaced the conventional (wet) batteries on my boat with 2 sealed gel batteries. (2 x 125 AH sealed calcium).

The link you gave is to ordinary maintenance-free lead acid batteries, not gel batteries. These batteries will have some sort of valve-regulated venting, so you shouldn't need to remove any bung whilst charging. If you've been given those instructions, you should query them with the supplier.

 

[alisdair4]

Finger trouble

You're right, they aren't gel- it's too early in the morning! As I say, the only instructions were to remove the bung (actually, a plastic cap over the vents). I'll query the manufacturer after the break.

 

[Seajet]

If your batteries have vents, regulated or not, I'd suggest you should supply proper means of upwards escape for hydrogen, not just a vague hope.

For instance on my boat I have a tube from the vent leading to a ventilator in the anchor locker above, so even when the ventilator is closed for sea there's plenty of contained space for the gas to escape to.

There have been some very nasty explosions due to battery hydrogen, the sort of thing which would spoil your whole day, or even cancel it entirely !

It would also be very worthwhile checking if the batteries you've got will leak when heeled etc.

 

[Plevier]

It depends on your charging regime.
If you have a multi stage ("smart") charger, yes you should have a vent as in some phases of charge you are likely to get significant gassing.
Under these conditions you can't regard the batteries as maintenance free. You will almost certainly need to find out which bit of cover to remove to top up. May be under the label.
If they are only ever charged at normal alternator or float charger voltage, 14V or so, any gassing will be negligible. Then they should be maintenance free.
Vents on this type of battery almost always have a microporous disc in them. This will stop spillage under most conditions. (It also stops any gas ignition flashing back into the battery and exploding it, like the wire gauze on a miner's lamp.)