Flat battery and car locked

[Barbanasos]

Hi,

I ve just been off for nearly three weeks and after coming back my 55amg has a totaly flat battery. I do not use the car daily which did not help before going on holiday. Which is the safest and appropriate way to deal with this?

Shall I unlock with the metalic part of the key? (What happens to the alarm as not even sure if the central locking will work hence only the drivers door will unlock).

When I unlock the car is it simply a matter of jump starting it using the positive connector at the front and somewhere on the chasis? I hope that does not affect the electronics, i.e does the key need to be out of the ignition when I attach the cables or at a particular position?

I hope someone can help.

Thanks.

 

[Norse]

I would not jump start the car if I was you. IMHO it is better to put a battery charger on the car and let it charge overnight.

 

[trapperjohn]

Agree with Norse. Lots of posts on here about guys locked out of cars and using a direct 12v feed to a "not so handy" connection point (blowed if I can remember where they are posted) Also posts on here about electrics going all Pete Tong if you jump start some E Classes. Could be just your "comfort" battery that is flat. Don't ask. I'm a 124 boy, I battery does all.

 

[Barbanasos]

Thanks guys. Lets see if any of our tech guys have any suggestions. I will ring the dealer tomorrow as well and seek advice. I hope dealer mechanics know what to do rather than start it and then start claiming that x,y,z parts will need replacing.

How bad can this be.

 

[Diesel Benz]

I understood this was a W210, a single battery then. And it would have jump start poles at the engine bay.

I would use a charger if possible. If not, then switch off both cars and connect the jump start leads first (the supplying car last). If you want to protect the supplying car, let it run and charge the battery some time, switch off and disconnect cables.

The essential thing is to try to avoid large loads and specifically sudden load changes seen by the alternator (when the car is running).

Finally, it is amazing how often jump start leads are connected with opposite polarity which of course is extremely bad (although some report that the car survived even from this, just a pile of fuses blown everywhere which is amazing too), better to be absolutely sure about the right connections.

 

[Barbanasos]

Thanks diesel benz. In order to be safe, I am not even touching the car. It has full MB service and rang today for mobilo life which is covered. They cannot book, so I will ring them on friday and see when they can attend on the day.

I think I will buy a new mercedes battery and get the guy from mobilo life to fit it. I ll see if he can bring it with him or I go and purchase myself in the morning and have it ready. My battery is totally dead so I might as well stick a new mercedes one in for the sake of £171.

 

[Barbanasos]

All sorted. Mercedes warrington had an offer on batteries so it only cost £130 for a new one. Mercedes 24h service turned up and sorted it all out.

This is for a totally flat battery. It was as expected advised not to jump start the car in these conditions. ALthough the drivers manual says so, it probably is for the case that the battery just does not turn the engine over.

Anyway this is how:

- Unlock drivers door using the manual key. (Battery dead so no alarm setting off)
- Pop the bonnet
- Use a trickle charger to the points on the right hand side of the engine bay, negative first, then positive, then flick the trickle charger on.
- The car has powered up so the alarm is going off. Press the key fob to unlock the car and stop the alarm.
- Then switch the trickle charger off, remove the cables from the engine bay and proceed to remove the rear bench to get access to the battery.

- Replace the battery and then reset windows and BAS/ESP by turning the steering wheel from lock to lock.

The guy did plug the car on STAR to run all the diagnostics to check everything. All good anyway and enjoyed a couple of hours driving after. Now I have to dispose the old battery.

 

[EDZ649]

This is a useful post, perhaps one of the mods could put it in the 'how to' section.