Battery / Charging Problem

Yesterday I had a flat battery, got a jump start and drove around for an hour to charge up, stopped the car and tried restarting battery still flat. Is the battery dead or the thingy that charges the battery?

Crunch..............

Reply to
Crunchie
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If it carries on running with the headlamps & the rear window demist on after you've jumpstarted it then the batteries dead

Reply to
Duncan Wood

If the battery was totally flat for some time, the car charging system often won't kick it back into life. Bench charging for several days *may*

- but the capacity of the battery will almost certainly be reduced. If it's more than a couple of years old, it's probably just as well to buy a new one.

Reply to
Dave Plowman

It could be either the battery not taking a charge, the charging system not producing enough power to recharge the battery, or a combination of both. Since they work togther, you should test them both. More information on battery testing can be found in Section 4 in the FAQ on

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Section 17 contain a troubleshooting guide for engines that will not start due to an apparent dead battery.

Kindest regards,

BiLL.......

Reply to
Bill Darden

The thingy that charges the battery is the alternator. Follow the largest wire from your battery + terminal to find it. It has wires connected at one end and a belt going round a pulley at the other end.

Invest a few pounds in a multimeter (£10) and connect it across the battery. The voltage should be about 2 volts more when the engine is running than when it isn't, if the alternator is working. If you get a difference smaller than 2 volts, check the connections on the battery are tight and clean first, then, if that doesn't solve things, remove, clean, and replace the positive and earth connections from the alternator to give a good circuit. I had a similar problem recently, replaced the battery, and still had the same problem until I cleaned the alternator's earth. It is possible, but unlikely, that the alternator needs replacing.

If you get no difference in the voltage, your alternator belt is probably broken. This would normally cause the battery light on the dash to stay on. They cost under £5 for most cars and take 20 mins to fit. I doubt you would have been able to drive for an hour if this was the problem, unless your car is a diesel.

If you get a 2 volt difference, the charging circuit is ok and the problem is with the battery. Before you replace the battery, first try topping up the fluid inside with de-ionised water from any decent car parts place. If that doesn't work, you will have to replace the battery. Make sure you get one with enough power for your car. The old battery will say on the top how many AmpHours (AH) you had, but it's usually worth getting a little bit extra.

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Reply to
DP

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