Batteries, and the non charging thereof

"Cé hé sin" (michael-m-mouse) 01/28/2015 at 17:27 • Filed to: Electrical

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For the past couple of days my battery hasn't been charging unless I apply some revs. Today it refused to start charging under any circumstances so I drove the five minutes or so home, stopped the car and tried to restart. After that five minute drive the battery had gone almost completely flat. Any ideas, apart from the alternator? I know that driving without charging will drain the battery but surely it'll last more than five minutes.

luvMeSome142 & some Lincoln! > Cé hé sin 01/28/2015 at 17:31

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Could be as simple as the alternator belt. If it was loose or slipping, that would explain the behavior of charging when revved.

over1g > Cé hé sin 01/28/2015 at 17:32

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Well how long the battery can last depends on many factors (ac/fans running, defroster, headlights, wipers, etc.). 5 mins is more than enough time to drain a not fully charged (and from the sounds of it, already tired) battery.

505Turbeaux > Cé hé sin 01/28/2015 at 17:32

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what kind of car?

thereisnospork > Cé hé sin 01/28/2015 at 17:33

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More specifically (and cheaper) than the alternator, could be the voltage regulator. Also could be something as simple as badly corroded battery terminals. Does the 'not-charging' idiot-light light up? On some cars the bulb is an essential part of the charging circuit: bad bulb = no charge.

You're right though, a fully charged battery should run a car just fine for a lot more than 5 minutes.

Cé hé sin > thereisnospork 01/28/2015 at 17:40

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Oddly, the light doesn't seem to light, but there's a voltmeter and it shows about 8 or 9v with the lights on. Before it used to suddenly rise to the usual 14 or so once the alternator deigned to alternate. It's the fact that the battery went completely dead after driving for five minutes that puzzled me.

Cé hé sin > 505Turbeaux 01/28/2015 at 17:40

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Mitsubishi FTO.

thereisnospork > Cé hé sin 01/28/2015 at 18:14

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Does it light up with all the other lights when you turn the key to 'on' when first starting up the car? The battery was probably not fully charged when you started your five minute drive - you mentioned the alternator had been iffy previously(?) and batteries can go from working to not without too much gray area in between.

RallyWrench > Cé hé sin 01/28/2015 at 18:16

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It sounds like your battery was already discharged, or has a sulfated cell preventing it from retaining a charge. If it reads anything less than 12.6V static it's discharged, and its life will be shortened accordingly. Normally I'd expect a basic fuel-injected car to run for at least 30 minutes on battery power alone, assuming no other consumers are on. I'm not sure if your alternator has a replaceable voltage regulator (most modern units don't) but based on your prior symptoms I'd look there first.