marthyh

Yesterday I came back from 2weeks work abroad, then I wanted to take the Benz for a spin .
No power to anything so doors don't open.
Luckily I could use the key (that tiny thing in the fob) to open the door,all the interiour lighting was still off, but upon pushing the 'start' button it fired right up.Obviously the starter baterry was fine.

After this drive,with no issues ,only joyjoyjoy. I parked it back up in the unheated garage and this morning everything was fine again, all systems are go.

Questions:

1.it it normal that the aux-battery in the rear compartiment discharges within 2 weeks time?

2.if yes, is it possible to mount a circuit breaker or such for the aux-batt.. and where? To avoid this in the future.Especcially when cold, my battery would freeze to dead without charge.

3 or is there another solution...

tonykharper

See above.

marthyh

Thanks! How many amps would you suggest and where to connect it please?

I know there is some 'plastic' cover next to/in front of the starter-battery. If you remove that rectangular cover: that should be the leads going into the aux-batt. (the + connector very close to the chassis)

Would that be it to connect to?

Then I would want to make something permanent: mount the charger under the hood or somewhere, so I only have to plug in the mains when I arrive, to stop for longer time...thus not to having to open the bonnet everytime.. any thoughts or suggestions always welcome.

tonykharper

This is what I use.

http://www.batterymart.com/p-del-021-0128.html,

I connect it to the starter battery or the aux battery but it mostly stays on the aux battery during winter. The connecting point is right under that plastic cover. Just leave the neg terminal connected to the battery and move the pos terminal to the tall pin under the cover.

I did not permanently mount mine to the car. I have it sitting on a shelf next to the car. I just lift the hood connect the two terminals and plug it in. About once a month I'll connect it to the starter battery until it goes green then I'll reconnect it to the aux battery.

Diesel Benz

Sounds like you missed the comment from tonykharper? If your car does not stay parked longer than a month or two, you should not need a permanent charger. You should figure out why the battery got flat in two weeks. Either something wrong with the car or some consumers where left on.

marthyh

Great info! I can live with 2 months of 'standby' time, but indeed 2 weeks seemed a very short time..

Have emailed the dealer and they offered to do a power-leak check, if it happens again (its still under Star-warranty).

Just out of curiousity: I have added two pix of the setup in the back.

Does this look OK to you: a 60 AH aux-battery(MB says its OK)

and that 7.5A fuse looks very un-original to me:

tonykharper

There is an easier way.

You can charge your trunk battery by hooking it up under the hood.

On the passenger side just left of the starter battery there is a black plastic box. Remove the cover and you will see the power points for the rear trunk mounted battery. The tall terminal, the one near the front, is the positive terminal. Connect your positive lead there and hook the negative lead to the negative terminal on the starter battery. If you want to charge the starter battery just move your positive lead six inches to the positive battery terminal. Hope this make sense.

Tony

Diesel Benz

That fuse did not come from the factory. Can you figure out what is it for?

marthyh

Not at the moment. I thought it wouldn't be from the factory, with those blue connectors etc.. thanks for confirming that!
I can only guess ..sat-tracker ??There are no crazy accessoiries afaik besides the standard option list.
Good that I bought the car from an MB-dealer with 6 months warranty,they do have the full history, since they sold the car new as well ,so if this issue plays up again, when I am back,
I get down there and start asking more questions ..and they will measure leak-current as they promised.

@Tonykharper: thank you for those instructions !