Battery drainage

[Rtaylor8]

Having taken the SLK off the road for the winter I usually attach it to a trickle charger and all is well.... however I took it out for a quick spin a few weeks ago and left the charger off when I came home. Trying to start it a couple of weeks later and the battery has drained - less than 9 volts.... (it was fully charged when I took it out). Any idea what the likely culprits are? I checked all the lights were off, radio off and air con/heater off when I got back. The car is in a garage so not exposed to the element........

any suggestions gratefully received

 

[Blobcat]

Something may not be shutting down, possibly due to water ingress. However not many modern vehicles will keep their battery charger for longer than a week

 

[joderest]

You could do a drainage test if you have a meter that will show milliamps, I think, but not sure (so check) disconnect negative and install meter between the negative lead and body, will show what is being pulled out.
You do not say how old the battery is, it could well be past its best, if you disconnect it, charge it to full and leave it overnight, if it drops down towards 12 volts or less, its had it. Good battery will maintain about 12.7 volts.
All modern cars will use power whilst sleeping to keep things going.

 

[Rtaylor8]

Thanks Gents... I have had the car 18 months, so not sure how old battery is... wasn’t an issue last year when I used everyday... so drainage must be relatively slow. Will try the trickle test, but also fully charge it and see.... appreciate that there will be some drainage with modern cars but seemed a lot over a short space of 2 weeks... if no joy will get a new one...Eurocar parts usually have a sale on!!

 

[sonic]

Check that the battery is being charged when running.