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MG MGB Technical - Charging batteries

Years ago, one of the service tasks was to check the level of the electrolyte in the batteries and replace it with distilled water. The acid had gassed off in the form of hydrogen and oxygen as the batteries were charged.
Some time later, along came "low maintenance" batteries which claimed they did not need topping up. They often came in translucent plastic cases which allowed you to see the levels of the acid without taking the plugs out. The levels did drop and the batteries did benefit from being topped up from time to time.

I have just bought a new battery (average price, not the cheapest, not the most expensive) with a great big sticker over the cell plugs. It makes no mention of maintenance anywhere on the casing. I have a few questions:

Do I need to take the cell plugs out when I charge it up?
Do batteries still appreciate being topped up with distilled water?
Are "low maintenance" batteries a thing of the past or are they all low maintenance now?

Fit it and forget it?


Years ago AFAIR you checked the level and filled it to cover the plates. Just do the same? Again the caps used to be vented years ago, now there is often a small tube with a pipe attached on modern batteries. As batteries are charged whenever you drive, it would seem the same as charging. I still have 2X 6v and just use a battery conditioner left on over the (low use) winter. i don't bother to loosen the cell caps.
Michael Beswick

If you *can* take the plugs out and see the level of electrolyte without breaking anything, then do so, it can't do any harm. Translucent cases were more to do with being able to check levels without unscrewing anything, like brake and clutch masters. If they had removable screw plugs then they were intended to be removed and the battery topped up as required. Some batteries are so-called maintenance-free and recycle evaporated electrolyte and I'd expect the caps of these to be sealed even though they may have 'coin slots' in the top. But I'd be very surprised if 6v batteries were anything other than 'remove the plug to check the electrolyte' types. The vent tube is used when the battery is located within the passenger cell, but I've only seen that on 12v types.
PaulH Solihull

These may not be 6v MGB batteries , however I keep mine on the conditioner and check the acid level maybe every other month. They hardly ever need topping up. With modern sealed 12v they are fit and forget. The charge process results in two hydrogen atoms being gassed out at one electrode and one oxygen at 't other. The idea is to build a case that can take the pressure and just to let them diffuse around until they meet up and react back to H2O. It always puzzled me that this wasnt how it was done but I guess it needed modern plastics and design tools to achieve in practice.
Stan Best

The only batteries on the market today, that require no maintenance, are the gel mat batteries. These are sealed units and can be mounted in any position that suits you, even upside down. RAY
rjm RAY

That all being said, I'd like to comment on one of the last little comments, "modern plastics..." - there is considerable difference in quality differences between cases.

Cases used to be heavier duty than current cases, and some are actually thin enough to almost breath.

Modern maintenance free batteries are as stated above, fit and forget. I haven't seen screw caps on a battery in decades. It used to be that one could boil out electrolyte in hot weather, to which one added distilled water. Sealed are less prone to this problem.

But I'm witnessing a new problem. I keep the top of battery clean to avoid across the top drainage between posts, so I couldn't understand why on my current battery the positive post was always so corroded, the green crud.

It was explained to me that the cases are so thin, that gas is escaping through case and this is the cause of quicken corroding. I'd like to know if others have heard this?

I'm going to have to discuss this leakage, and the availbility of screw cap batteries, with a battery supplier I know - fortunately it will be over beer, not electrolyte.
R.W Anderson

I'm still installing "screw top" batteries in customers cars as well as my own. They still make up a major portion of the new batteries that are sold today, mainly due to the lower initial cost. It would seem that you are witnessing out gassing that is mixing with oxygen and corroding your battery terminals. The simple cure is to lather the battery terminal with petroleum jelly before and after you install the cable terminal. This sets up a barrier that prevents the oxygen from reacting with the gases of the battery as well as the lead of the terminal. RAY
rjm RAY

Thanks Ray...

I must live in a cap free zone when it comes to batteries. Now I'm curious enough to stop in a few stores and actually look around again at what is selling.
R.W Anderson

This thread was discussed between 30/11/2010 and 01/12/2010

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