battery is so dead, battery charger is reporting it as full.

seatbeltnoob

reall strange one, wifes car seemed fine, it cranked first time every time and now today she went to the dentist and it won't start. it won't even crank, wife tried it a few times and it got so bad that it wont even lock the car.

Whenever friends and relatives have this situation - where car wont start at home, I don't even bother to jump start it, I just take the battery out and charge it at home. Usually the battery got run down due to too many local journeys it never gets a chance to charge up fully. So a nice long 5 hour charge is the best thing.

I didn't test it with a multimeter or anything, but when i plugged it into the charger it was showing full. That was bad news because the way the car was behaving if it wasn't a bad battery it would have been a major ECU issue.

I thought about just putting my car battery into it and seeing if it would start - I'm glad I did because it started fine. So a new battery was ordered. Glad I didn't tow it to a garage based on initial suggestions by the battery charger.

So what does that mean? Why would the battery charger report it as full but doesn't hold enough charge to operate the cental locks?

Battery came with the car, wife owned the car for 4+ years so it's done it's duty.

onlyfoolsandparking

It might well report it as 'fully charged' but if it's a tired battery it wont hold that charge for long, also is it a decent battery charger or (with respect) a cheap one, that can make all the difference to whether info reported is factual.

4+ years is not bad for a battery, your right it definitely did it's duty.

Goudy

This is called acid saturation.
The acid in the electrolyte solution drops to the bottom over time so there's less acid in contact with the plates.
This leaves a watery electrolyte at the top that causes corrosion of the plates.
In the old days owners used to test electrolyte in their lead acid batteries with a Hydrometer to see what the density of the electrolyte was and if needed, replace it. No one bothers these days as most batteries are sealed or use different technology to store the electrolyte like absorbent glass fibre matting.

It happens as the battery gets older with repeated discharge and charging and the battery will often feeds back 12-14v to the charger so it thinks it's charged, but you need more than volts to start a car, you need amps as well but now the electrolyte and the plates are no longer up to storing them.

caprikid1

Some battery charges have a flat mode that can get round this. I also sometimes find an old skool battery charger that does not check anything can work. I had a similar situation with a classic car last night, non of my battery chargers would register anything it was so flat and would not attempt to charge. Solution was I jump started it with a jump start battery , left it running and then put the battery on charge, the alternator had got enough charge into it for the chargers to work normally. Seems fine again. Revived many a dead battery using the above methods, my Caterham was especially prone due to them miniscule size of the battery.

Biggus_Dickus

A multi-meter may give you an indication of 12v (‘ish!) across the battery terminals but a multi-meter draws minimal current. It isn’t a real test of the battery’s ability to deliver a large and sustained amount of current ( i.e. Amps).

You need a battery load-tester to establish the car batteries’ fitness for purpose'.

 A load-tester draws a large amount of current and ascertains if 12v (or thereabouts) has been maintained.

If a battery is in poor condition the voltage/amperage indicated on the load-tester will quickly drop away.

frost500

Have you checked the earth strap?

Ectophile

Sometimes a battery will suddenly fail, as a connection breaks loose inside it.  The voltage may appear normal, but the moment you try to start the car, the voltage collapses and loads of warning lights appear on the dashboard.

Once that happens, there's nothing you can do to save the battery - it needs replacing.

seatbeltnoob

It was with the car when my OH bought it, over 4 years old at the least (perhaps older). I just replace dthe battery.

Multimeter was reporting 12.6v but multimeter can't really tell the whole story because it's about the cold cranking amps rather than volts.

Rolandtheroadie

Charged a motorbike battery around 3 months ago and it said fully charged within around 5 minutes. It wasn't. 
 Put it on a turtle charge, took a few hours then said full again. It's been ok since.