Leisure battery leakage problem.

[Jimma]

I have a 110ah M-Tec leisure battery installed between the driver and front passenger seats of my T25, next door to the regular battery. I have a bulkhead between the front and back of the van so the battery sits flush against that. Somehow the battery seems to have leaked fluid onto the bulkhead, causing a couple of areas of paint to flake off and corrosion to turn these areas white and powdery.
The battery is charged though a charging relay that connects it to the main battery when the engine is on. I have put a volt meter across is while charging and it reads 13.75 volts which should mean it isn't being over charged and boiling, but even if it was I can't understand how it can be leaking along the top rear edge of the battery casing.
There doesn't seem to be any issue with the main battery at all, only the leisure.
I have removed the leisure battery and cleaned it and the van up. I have checked the fluid level in each of the battery's cells and all is fine. It is now on charge in the house and I simply cannot see how the leak has occured in the first place.
I was just wondering if anyone else has experienced anything like this as I am wary of returning the battery to the van, only to have it cause more damage but don't want to chuck it out as, apart from this, I have never had any issues with it.
Any advice would be much appreciated.

[Mocki]

are you sure its not just the vent pipe ?

[jamesc76]

If its over charging then it could be venting a small amount of liquid out hence the paintwork wear!

[Oldiebut goodie]

Any gas that comes off of it will tend to condense on the colder metal nearby - that gas is corrosive!
The battery would be better enclosed anyway - I wouldn't like to have exposed terminals next to me in the front. One spanner drop whilst the engine is running and kiss your donkey goodbye! Yes, it does happen - the very least you will get away with is acid burns.

[Jimma]

Thanks for your comments. Having charged the battery indoors overnight, I have discovered that it is spitting liquid from the vent hole on the left of the casing and this is somehow spreading right round the lip at the rear of the battery. There were also droplets of fluid on the area around the battery and it was making fairly loud venting noises, alongside a bubbling sound. A small amount of liquid also seems to have escaped from the fill holes even though they are screwed on tightly.
The battery is about five years old but has never been used heavily so goodness knows what has gone wrong with it but I guess it's time for a replacement, which is very annoying.

Oh and Oldiebut goodie, I have the positive terminal on the battery completely insulated so as to avoid any such spanner incidents. Very worthwhile advice though.

[kevtherev]

five years is the life of leisures I'm afraid.
It would have had to be replaced sooner rather than later anyway