S40 repeated dead battery

[1988GP]

Hi,

I have a 2006 s40 1.8 petrol which had a replacement battery two years ago.

For the last 4 nights the battery has drained to a point where the car won't start. I just drained again after leaving the car for approx 2 hours today,meaning something is draining it very quickly.

Had the battery checked at garage and it charges fine, however the 'Alarm System Service Required' message has appeared for 2 of the last 4 jump starts. Is this common?

Any other ideas? Done 4 lots of 50 mile trips this week so has had enough time to charge.

Thanks in advance for responses

[kerrgreg]

When driving the car, does the battery light go out?

[1988GP]

Yes, no lights on dash

[msh]

Hi
have you checked the voltage across the battery with the engine running 13 to 14 volts
the alternator may be on the way out the have been known to smoke when they burn out
check after a good run wait 30 min and touch the alternator if hot this could be your problem
Mark

[Powerforge]

another useful test if you have a clamp meter is to measure DC amps being drawn down the positive lead with the ignition off - should be fractions of an amp or you have something live that shouldn't be.

Make sure to check for the classic dodgy boot/interior/glavebox switch that lets a bulb run constantly..

Had an old transit that did the same as you describe - turned out the diode pack on the alternator had failed so the battery was discharging through it !

[oragex]

Originally Posted by 1988GP

Had the battery checked at garage and it charges fine, however the 'Alarm System Service Required' message has appeared for 2 of the last 4 jump starts. Is this common?

the alarm siren module has a small battery inside that commonly leaks after a while and melts the circuits inside. could cause a short. you could try disconnecting the module and see how it goes

[geoffco]

Originally Posted by oragex

the alarm siren module has a small battery inside that commonly leaks after a while and melts the circuits inside. could cause a short. you could try disconnecting the module and see how it goes

The 'Alarm System Service Required' message is also an expected result of the main battery being totally drained (because the alarm battery isn't getting charge) and disappears on its own after the system gets fully charged...

Geoff