This week it seems the battery has given up and it looks like i'll be buying a new one but I want to know if there is anyway to check if there are any other problems that are draining the power.

I went to start it monday morning with no luck, after work I got a jump and had it running for a bit, alternator seems fine as I got 14 point something on the volt meter with the engine going. It started fine this morning, but when It came time to go home it wouldn't start again so I had to get a jump.

As I say, I reckon the battery needs replacing but I really don't want to replace the battery and have the same problem again.

I got some good advice in this thread


cheers

Fred W B


[Edited on 23/4/13 by Fred W B]

Symptoms generally point to a dead cell in the battery sometimes called a gassing or shorted cell, the way to test the battery is to measure the voltage drop when the battery is under very heavy load (100 amps +) for a few seconds . Most garages and motor factors that sell batteries should have a tester I use one very similar to this ebay Item number: 120994425153



If the battery is u/s the voltage should drop instantly from about 12.7 volts to 6 volts and stay there, but sometimes it may slowly rise to about 8 volts as the battery heats up.

On battery discharged but otherwise healthy the voltage starts below 12.7 and falls to about 8 volts gradually.

A healthy battery will fall quickly to 9 or 10.5 volts and be able to hold that voltage for several seconds, continuing the test for longer will damage the battery.

You can simulate this test by allowing the battery to rest for a couple of hours then disconnect the coil to prevent the engine from starting, if the battery has a decent charge it show 12.75 to 12.8v with no load if when the engine is cranked the voltage drops instantly to below 10v to 6v it indicates a battery problem.

The quick and dirty way to check for a current leak is simply to disconnect the battery overnight. If after 12 hours the battery starts the car then it suggests a current leak. The first suspect is usually the alternator diodes so try disconnecting the main alternator lead overnight *remember to reconnect before starting*.

Alarm and immobiliser systems, CD head units and boot lights are the next suspects tbut racking down current leakage gets tricky the one thing to keep in mind most DMM have an internal 10 amp fuse and if it blows when testing it give no indication it has failed.



[Edited on 23/4/13 by britishtrident]

Thanks for the tips. I'll do some tests tomorrow. I was hoping the first time it was a light or something left on but theres nothing obvious. I left the car for a week last month and had no trouble starting it which is why I thought the battery had died.

Would I still be getting a charge if the alternator diodes were gone? The warning light for the alterner runs it's normal test then goes out. Would I have to remove the lead from the alternator itself to check it as it's not somewhere I think I can get.

If only one diode is leaking an alternator will stil charge at a reduced rate, however it still looks more like a battery fault.

Thats really what I was hoping to hear. With buying a battery when you've got a choice, do you just go for the biggest amp hours?

I put the meter across and it seems to draw a current of about 40 mA when off, so that seems fine based on what I read in the other post, problem now is getting the old battery out, it was so much easier doing one in the boot of a car.

I got a new problem now, the securing bolt sheared.

[Edited on 24/4/13 by morcus]