VW Passat battery trouble. Help needed.

internelligent

I'm almost convinced that my battery needs replacement but I wanted to post here all the information I have on the problem and see what everyone else thinks as the last thing I want is to have a new battery going dead on me.

Anyway, here 's what I have:

Car wouldn't start.
Used Jump leads and it started fine.
Drove it around for 30 mins.
Turned it off and immediately turned it back on and it started again.
An hour later I drove the car for 10 mins, left it off for about 30 mins and then it wouldn't start.
Checked voltage across battery - 9.75V
Used jump leads again and checked the voltage across the battery terminals - 14.3V so that looks like the alternator's good
When I turned off the engine and checked again the voltage was 12.5V - also good.
Disconnected cable from positive terminal and left overnight.
Checked voltage of battery next day - 11.2V
Re-connected cable to positive terminal
Car wouldn't start
Checked voltage - 9.75V
Disconnected cable again and re-checked voltage - 10.02V
Checked resistance between positive cable and earth - 1.5Mohms

From this information could it confidently be said that the battery, and ONLY the battery, is the issue here or are there any other checks/tests I can do to fault find it further? Rather not get ripped off by a mechanic!:(

Bandara

internelligent wrote: »

I'm almost convinced that my battery needs replacement but I wanted to post here all the information I have on the problem and see what everyone else thinks as the last thing I want is to have a new battery going dead on me.

Anyway, here 's what I have:

Car wouldn't start.
Used Jump leads and it started fine.
Drove it around for 30 mins.
Turned it off and immediately turned it back on and it started again.
An hour later I drove the car for 10 mins, left it off for about 30 mins and then it wouldn't start.
Checked voltage across battery - 9.75V
Used jump leads again and checked the voltage across the battery terminals - 14.3V so that looks like the alternator's good
When I turned off the engine and checked again the voltage was 12.5V - also good.
Disconnected cable from positive terminal and left overnight.
Checked voltage of battery next day - 11.2V
Re-connected cable to positive terminal
Car wouldn't start
Checked voltage - 9.75V
Disconnected cable again and re-checked voltage - 10.02V
Checked resistance between positive cable and earth - 1.5Mohms

From this information could it confidently be said that the battery, and ONLY the battery, is the issue here or are there any other checks/tests I can do to fault find it further? Rather not get ripped off by a mechanic!:(

Hi

I am absolutely hopeless at mechanical stuff but my wifes 00 Passat does fairly similar acting up to yours, we might solve both our problems here.

Put the key in and start it and it starts and dies immediately (within half a second), start it a second time and it does the same, on the third of fourth time it kicks in and drives fine. The next time you start it might do the same it might not. I'd estaimate that over 60% of the time it won't start until 3rd attempt. I've had 3 mechanics look at it, one replaced a fuel sensor of some description, another replaced some engine temperature sensor, the other just admitted defeat.

The problem is still there to this day. Car has 120k miles on it if thats relevant.

Captain Slow IRL

Check for a currant drain with an ammeter - you should have less than 0.1A.
(Disconnect one of the battery leads and connect it in series.)

If you have more than 0.1A, start removing fuses and observing the currant reading to single out the culprit.

Edit - how old is the battery anyway?!

Mr.Diagnostic

internelligent. You need a new battery

Hammertime. You need a new mechanic

Bandara

Mr.Diagnostic wrote: »

internelligent. You need a new battery

Hammertime. You need a new mechanic

lol

for once I did actually laugh out loud.

internelligent

Cheers for that. The battery is about 5 years old which points yet again to a battery change. Just wanted to save myself from cash. Thanks for the replies!