Flat Battery

garethgas

A flat battery can often be a symptom of another fault. If you just replace the battery, it will be fine for a while but the underlying cause will still be there.
It could be an alternator problem, a bad earth, a faulty light switch in the boot or some other unidentified drain on the battery.
When I bought my car, it had a new battery supplied by the AA, (indicating a breakdown) by the previous owner. After a few months it kept going flat every few days.
Found out there was a part (cant remember what) that was faulty and drawing current when switched off and draining the battery.
I suspect this was the fault all along but people are too quick to jump to the conclusion that the battery is faulty.
I'm not saying it isn't the battery, just that it could be so many other things too so its worth getting it checked properly.

birkee

garethgas wrote: »

A flat battery can often be a symptom of another fault. If you just replace the battery, it will be fine for a while but the underlying cause will still be there.
It could be an alternator problem, a bad earth, a faulty light switch in the boot or some other unidentified drain on the battery.
When I bought my car, it had a new battery supplied by the AA, (indicating a breakdown) by the previous owner. After a few months it kept going flat every few days.
Found out there was a part (cant remember what) that was faulty and drawing current when switched off and draining the battery.
I suspect this was the fault all along but people are too quick to jump to the conclusion that the battery is faulty.
I'm not saying it isn't the battery, just that it could be so many other things too so its worth getting it checked properly.

The alternator will support the loads on the car, and should replace a discharge caused by a faulty item very quickly when the engine is running (unless the car isn't used for days.)
i.e. A boot light should run for days.

Replace the battery. It may still be 12v, but the Ah capacity has probably gone down from near 40Ah to just a few AH. Caused by sulphated plates, a particular problem when batteries are left in a semi discharged state. i.e. Lots of short journeys, using lots of starts, that doesn't replace the charge used starting.
It's bit different now with alternators, but I seem to recall that the quoted driving time before, was 20 miles to replace the charge removed by starting the car.
Lots of short journey starts? Charge the battery at weekends.

Strider590

garethgas wrote: »

When I bought my car, it had a new battery supplied by the AA, (indicating a breakdown) by the previous owner. After a few months it kept going flat every few days.
Found out there was a part (cant remember what) that was faulty and drawing current when switched off and draining the battery.
I suspect this was the fault all along but people are too quick to jump to the conclusion that the battery is faulty.

Generally speaking, if a battery is older than 4 years then it should be the first thing you replace.
If it's less than 4 years old and has been sat for a few months allowed to self discharge (on a garage forecourt for example) then it could also be ruined as mentioned in the post above re: plate sulfation.

Current drain on the battery is quite easily diagnosed by disconnecting the battery from the car and seeing if it's works after the time period that would normally see it flat. Finding the faulty part requires some specialist knowledge of that particular model of vehicle and it's "common faults". However common faults across most vehicles include the alarm system and door switches for the interior lights (most often the boot, where you can't see it).

[Deleted User]

I'd guess that the current battery is either the original or it has been in at least 5 years as it looks old/dirty. I've ordered a new battery online so hopefully that sorts it.

[Deleted User]

Just an update...

I put the battery back in after it had been charging over night and car still wouldn't start. I borrowed a working battery and car started OK with that.

I do hope it is just a well and truly knackered battery and not some underlying fault with the alternator or something.

garethgas

In that case, your going to need a new battery anyway. Hopefully thats all it is and you'll be fine.

chris175

As a quick check for the alternator why not put a multimeter across the battery with the engine running and all lights + heated rear window on? Should see 13-14 volts. Much lower and alternator is struggling.

[Deleted User]

chris175 wrote: »

As a quick check for the alternator why not put a multimeter across the battery with the engine running and all lights + heated rear window on? Should see 13-14 volts. Much lower and alternator is struggling.

I haven't got one but think I will invest in one. Cheers.

Strider590

Deleted_User wrote: »

Just an update...

I put the battery back in after it had been charging over night and car still wouldn't start. I borrowed a working battery and car started OK with that.

I do hope it is just a well and truly knackered battery and not some underlying fault with the alternator or something.

Your quite lucky the thing didn't explode on you...... I can only assume there was a reasonable delay between removing the charger and trying to start the car!
Dead batteries produce a lot of hydrogen gas when forced to take a charge, it sits in the top of the cells and in the vent covers, one decent spark (either internally or from the terminal posts) and it's battery acid shower for you and half the street.

Seeing as your ok im just saying this for the benefit of anyone who comes searching through this thread in future.

[Deleted User]

Strider590 wrote: »

Your quite lucky the thing didn't explode on you...... I can only assume there was a reasonable delay between removing the charger and trying to start the car!
Dead batteries produce a lot of hydrogen gas when forced to take a charge, it sits in the top of the cells and in the vent covers, one decent spark (either internally or from the terminal posts) and it's battery acid shower for you and half the street.

Seeing as your ok im just saying this for the benefit of anyone who comes searching through this thread in future.

I switched off the charger about two hours before actually getting round to putting it back in the car.

:beer: