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MG MGB Technical - Battery over-charge?

On a battery charger, can a battery be over-charged or does it just reach a point and not charge any further?

Does it hurt the battery to charge it too much?

If it's any bigger than a trickle charger it will cause the battery boil over and I assume it is overcharging at that point.

Clifton Gordon

This all depends on the design of the charger, however a constant current one will overcharge a battery. The fast chargers can buckle plates with the sort of wattage they dunp in. We went out in our B today, it had stood for a month and had full charge and started fine, I have an intelligent charger.
Stan Best

I forgot and left the charger on all night (the B had been sitting for about 10 days). 'Didn't hurt a thing --- it has a tapering charge that begins at 10 amps and tapers down to nothing.
Dan Robinson

Depends on the maximum current and voltage that the charger puts out. The higher the open-circuit voltage at the charger terminals the higher the current it will push through the battery. More than 15v and it will still be pushing a current through the battery when it is technically fully charged, which will cause it to bubble (boil) which will evaporate distilled water from the cells and lower the level of electroltye. Between 13v and 15v i.e. trickle charge the battery will only be charging at its normal rate when on the vehicle with the engine running.

With trickle chargers leaving it on overnight shouldn't actually cause any harm, but it may boil out a bit of distilled water. 'Rapid' or 'boost' chargers use higher voltages and currents and these can cause more damage, like buckled plates. Even a trickle charger shouldn't be left on more than overnight at the most, if you need to leave it on longer i.e. for occasional use you should get a 'conditioning' charger which senses the battery voltage and turns the charge on and off automatically as required. However unless you have a power-hungry alarm, or some other drain, the battery should hold its charge sufficient to start for a minimum of a month.
Paul Hunt 2

I had a problem for some time in my '72 Roadster where there was a peculiar smell at times and the battery would not hold charge. After doing all the normal testsI recently checked the battery voltage whilst on the move and found it was jumping from a regulated 14.6V to a decidedly unregulated 17.5V, changing at no particular point, like a bump or high/low revs. The battery did not appreciate the latter which I now believe is due to a fault in the alternator regulator.
If you have a slight smell of burning (my wife's description) then it could well be the smell of the boiling activity, (or something more serious!!) so put a voltmeter on the battery terminals and take it for a run.
Richard Coombs

This thread was discussed between 19/11/2006 and 21/11/2006

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