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MG Midget and Sprite Technical - how do you test a battery charger

Hi all

I replaced two batteries on different cars within the last year and both now don't seem to respond to my previously reliable charger. So I wondered how you check a battery charger. if you have any ideas please make it an easy to follow suggestion as me and electrics fell out years ago !
P Bentley

does it have an ammeter on it? does the needle move? if you attach the croc clips across a test bulb and switch the charger on does the bulb light?
David Smith

Hi David.
No it doesn't have an ammeter, just a system of traffic light bulbs essentially. will try the bulb idea later and see how I go.
P Bentley

Clip croc clips on your tongue and energize charger.

If you do not leap into the air, the charger is goosed...
Mark O

I'm sure I remember reading on here before that some chargers won't charge a completely flat battery?
As for checking the charger Just touch the two clamps together and see if they spark.
Good luck
Dave Pratt

I'm sure I remember reading on here before that some chargers won't charge a completely flat battery?
As for checking the charger Just touch the two clamps together and see if they spark.

I suspect both batteries are completely without any juice at all. . .I wonder if the shop that sold them to me will have a suitable charger to sort this (both are Yuasa batteries) which I have not had problems with before.

Will report back.
P Bentley

PB - ref the 'system of traffic lights' - is what you have a Charger or a Conditioner?
David Smith

well I always thought it was a charger. . .embarrassingly I will have to check now you have asked !
P Bentley


I remembered the old-fashioned way of resurrecting stone-dead batteries. It's called parallel charging. It takes a while and you need another good battery, the bigger the better to do it with.
(This article suggests at least 2x the capacity, expressed in Ah).

For clarity's sake I found the following site which shows the procedure.

I have a 3 channel smart charger I bought for my boat which has a desulphation function. In effect it zaps the battery with a spike (IIRC 48Vdc) which breaks up the solid sulphate deposits on the plates which is what commonly kills batteries. Mine was expensive, but they are much cheaper now for a single channel smart charger and I have seen them bring batteries back from the dead.

As mentioned in another recent thread I was taught not to store batteries on a concrete floor - it's supposed to kill them in short order. I do not understand why that should be, but I always store them off the floor on a wooden pallet or similar and have no problems.

As a quick test of your charger (which was the original Q) you could test the unloaded voltage of a known good well-charged battery with a voltmeter; then connect the charger and switch it on and test the voltage again. The battery V should be over 12Vdc, say about 12.5 or so. The charger volts should be in the order of 14Vdc if it's working. As your batteries are so low the charger won't even recognise them as 12V batteries and won't attempt to charge them, so you need somehow to bring the battery V up as described in the article.

Best of luck!
RS Hughes

Thanks for the video link RS Hughes. I have success ! albeit that I did a version of your helpful video link by running my daily hack at idle for 20 mins, and having used jump leads to my dead battery. This gave enough charge for my charger to complete the job. hey presto the task was done.

Appreciate all the advice given guys, be in touch with my next drama shortly !!
P Bentley

Aah - good show PB!
RS Hughes

gday, FWIW Modern batteries are not expected to last more than 5 years, desulphation is only a short term solution. The real problem is that the battery plates shed metal and oxides leading to an internal short and then discharges by itself. Cheers Rod
R W Bowers

This thread was discussed between 22/05/2015 and 30/05/2015

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