SLK320 Parasitic battery drain?

[pTang]

Hi all,

First post, so please be gentle!

I've had an '03 SLK320 from new that doesn't travel much - it's a weekend toy. Until about a year ago it was good as gold but then travelling up past Peterborough the car cut out on me. Totally dead battery. MB Assist rescued us and it turned out to be a defunct alternator regulator.

Over the past few months the battery seems to go sub 10v after two days of being in the garage. I jumped it from my other car and drove the 15 miles down to the dealer in Bedford. They ran a full battery test - all cells ok - and an alternator test - all ok. So the battery recharged fine on the run down there.

Seems I must have a large drain somewhere, so out with the multimeter. My parasitic drain seem a tad high at 112mA. My first thought was the radio playing up (as I've had in other cars) but minus fuses 5 and 8 the drain only dropped to 110mA. However, pulling fuse 9 dropped the rate to 33mA.

The fuse box contents says #9 is for roof light (which was turned off), horn, alarm and boot light (not fitted). Is there anything else?

I do have a trakker fitted and even although I'm not supposed to know where it is, I happen to know that the trigger is run against the fuel pump power line.

So my questions, what is the usual drain when sitting on a drive? Also, do trakkers also have a main power pickup somewhere to recharge its own battery or is it all run off the single feed from the fuel pump?

Thanks in advance.

'tang.

 

[Diesel Benz]

If the battery drain was 112 mA and the car was parked for 48 hours, you would loose 5.376 Ah capacity from the battery. Less than 10% of a good battery. I'm assuming you have occasionally some larger drain but it just did not happen when you measured it.

I'm not familiar with the tracker but perhaps you got the tracker powered off when you removed the fuse #9? Does the car have an alarm system? 33 mA sounds a bit low for a car with an alarm fitted, but it should be less than 80 mA typically (I don't have the figures for an SLK).

 

[pTang]

I had a chat with Tracker yesterday and they say the unit I have should only draw 15mA when 'ignition off'. However, the unit should be serviced every 5 years (they admit they hide that in the small print in the handover document). So first step is they're coming to do the service on the unit/change the backup battery and at the same time I can get an accurate drain reading for it.

If it's not the tracker and it's not the radio then I think I'll get the local dealer to try to track it down during the B service as it can only be the factory fitted alarm (or other fuse #9 device).

I am a little bit concerned that one of the battery cells may not be holding a charge. When the dealer tested it, I had just driven 20 miles quite... enthusiastically. If I leave the car with them over night they can retest each cell in the morning.

I had a new battery fitted in Nov '07 - do they come with a 2 or 3 (or even 5) year warranty?

'tang.

 

[killwilly]

An interesting point, how long should a new battery last? When I recently sold my 9 year old BMW, it was still on the original battery and it would stand for up to a week without use.

 

[pTang]

I now have a fully working SLK back in the drive!

Tracker gave my unit an overhaul and the idle drain was within normal ranges.

The battery on the other hand did have a dead/dying cell. After a run, it held enough charge to restart the car but after 2 hours was below the minimum for the car to start.

During the service they traced the hefty drain to a faulty alarm sounder unit as suspected on fuse #9 - it was drawing a large current when idle for some reason.

So, one new sounder and one new battery and we're good for a summer of driving - oh, where's the sun gone?

Thanks all for your help.

'tang.

 

[maxima]

from my experience - 95ah MB battery - 3 yr warranty and with the drain I have and weekends shopping driving only - 4 yrs is about normal life span for it..