alexander12m12

Unfortunately, a friend of mine has a 2004 E320 that seems to have a dead battery. As he was trying to charge the battery he managed to lock the key in the trunk without a spare. The car itself is unlocked with a dead battery. However, there is no way to get into the trunk without the key any help would be appreciated.

Things that I have tried when I went to my friends house.


1. Pull the lever on the driver side.
2. Take out two fuses from the fuse box on the driver side hope to reset the trunk function and reinsert the fuses pressing the unlock button.
3. Give a little juice to the battery under the hood.


Last resorts?
Request for a new key
Punch out the keyhole?

jimbo1763

I have never used one (disclaimer), but I note that a lot of trickle chargers these days come with the ability to plug into the cigarette lighter. Left on long enough, I wonder if that would give the battery enough oomph to allow the electronic opener to work. You might want to check-it may be that the cigarette lighter has to be fused to allow for the "always on" option to do this. There are lots of posts here on how to do that.

A trickle charger costs a lot less than a new key.

cetialpha5

Or take out the little battery in the front to a store like Autozone or Advance Auto and have them charge it up. They usually don't charge anything to do that. Then you might have enough power to pop the trunk.

wjcandee

Yeah, the Yuasa AGM Aux battery charges in an hour at the 6 amp setting.

A couple of thoughts: (1) The electrical system has two stages of cutting off consumers as the voltage in the system declines. So with the key ON but the main battery dead and the car not running, both stages should be in effect before it switches on the AUX battery. The (front) cigarette lighter is cut out during the second stage, so it MAY not be possible to put juice in the rear battery through the cigarette lighter, even with the key ON all the way. If you try it and it works, let us know because that would be good info to have. Second, the trunk auto-close on cars with that feature is cut out during the second stage as well. Accordingly, juicing the AUX battery might not power the lock handle that opens the trunk. But it might. Again, if you get it to work, let us know. That is certainly worth a try.

(2) Attached is the technical explanation of the battery system, straight from the horse's mouth. I wouldn't try to jump the car there. Indeed, Mercedes forbids it.

(3) If your friend needs a new battery, here is probably the best deal: $145 for an AC/Delco Professional AGM battery, with free shipping. There is also a good deal from Rural King, which is $139 plus shipping. But you get a $20 rebate from Exide, the manufacturer, which will help cover the shipping. And they may not charge you sales tax as Amazon does. So the Rural King Group 49/H8/L5 AGM, made by Exide, is at: http://www.ruralking.com/battery-auto-agm-rk-agml5-49.html

(4) If your friend needs a new AUX Battery, here's the best one, from YUASA, an exact fit AGM battery size YTX-14BS. I have also included the sheet below on how to install it.

cetialpha5

I believe there's also a fuse that you can move that will leave the cigarette lighter powered even when the key is off so in theory you might be able to charge the battery if you can figure out which fuse it is to move.

Also if you need a battery now, there are probably 3 local options, Pepboys, Autozone or Advance Auto depending on which one is near you. Pepboys just has 25% off right now so their $200 battery is $150, they charge to install the battery now though. Seems like they have 35% off every few weeks which would bring it down to $130. You can use a discount code at Advance Auto like TRT30 which takes 30% off up to $50 so their $189 battery comes down to $139 and they install for free. Autozone has it for $172 with a 20% off code (spring) brings it down to $137.60. Advance auto has the slightly bigger battery, 900 CCA vs 850 at Pepboys and Autozone, but I believe factory is 850 cca.

wjcandee

As to the fuse, true. It's obvious which one it is, as it's one of two fuses in the driver side under the hood fuse/relay box that can be set to the right or left in its slot. One could set both and be in business. If it's in line with the other fuses, it's in the disabled-by-key position; if it's offset, it's constant.

That's a nice summary of the better retail options. I have that Advance battery in the ML350 -- installed it myself several months ago. It's a fine battery, a good deal, and most Advances will install it for free in a W211. They are very, very nice people at my local Advance, and well-trained, and I like giving them my business.