MG Car Repair: MGB 1974 Roadster USA, 6 volt batteries, trickle charger

Question
I am restoring a mg with 2(6 volt)batteries and for the second time a battery has exploded. Car was running fine last fall but when left for a while it went dead. As it was winter I did not try to charge batteries. Just now as I tried to charge I noticed that sometime between the begining of winter and now it exploded. Could this be an electrical fault? I dont this to keep happening. Prior to my getting the car it sat for ten years in a barn. Should I convert to a single 12 volt system?

Answer
Leaving your batteries all winter to go flat is the worst thing that you can do to them.  Brand new batteries can be ruined in one winter.  Once a battery is damaged, any attempt to charge it can cause it to explode, especially if you use a high-current charging unit.  If you are going to leave a car over winter in future, I recommend that you connect a small trickle charger to keep the batteries topped up.

I don’t think you have an electrical fault, but you could check for a drain current by detaching the earth lead from the battery and inserting an ammeter between the battery terminal and the cable.  Switch everything off, including the courtesy lights.  If you have an aftermarket immobiliser, disconnect it or remove the fuse.  Now check for a current.  Anything greater than a few milliamps must be traced.   

There is nothing wrong with having two 6-volt batteries, apart from the cost.  I routinely change to a single 12-volt battery because they are cheaper to buy and easier to obtain.  You may have to enlarge the access hole slightly, and you will probably have to flatten the L-shaped reinforcing strip at the base of the battery carrier.  In the UK, battery types 063 or 065 will do the job nicely.