I noticed last winter that the AGM batteries in the E320 CDI and S550 4matic were severely taxed while the vehicles were in storage. I had to replace the battery in the S550 after only five years of use. The manual for the S550 actually says to charge the batteries while the vehicles will not be in regular use.

Meanwhile, the traditional '95 E300 can sit outside during the winter for 6 months with a 2010 battery and will start right up.

Anyway, I decided that I need to charge the batteries in the newer vehicles because of the battery drain inherent in the new designs.

MB branded chargers are made by CTEK which is a Swedish company that manufactures chargers. CTEK makes a lot of different models and you have to make sure and get one rated to handle the large batteries our diesel's have (> 95 Ah). The MB branded ones at the dealer are expensive ($175+)!

I found this one to be the correct size and this particular one was the best priced new one I could find after going to a bunch of sites (seller also shipped it quickly to me):

CTEK charger suitable for our MB diesel batteries: MUS 4.3

This charger comes with two connection method's: clamps and eye rings. For the E320 CDI (or any vehicle with difficult to reach battery in trunk), I recommend hooking up the eye rings to the battery post bolts and snaking the wire out to a convenient place in the trunk. You then just connect the charger to the wall, connect the charger to the connection point (after removing the rubber protective cap, and then set the charger to charge).

Warning: do not run the "Reconditioning mode" with the charger connected to a battery and vehicle due to the higher voltage used. The newer diesels have very sensitive electronics and electrical systems! This mode might shorten the lifespan of the electrical system of the car.

The CTEK unit I purchased is very well made and thought out. I can see why MB approves of these!

The newer MB's use quite a bit of energy even when not running and this puts a lot of strain on the batteries. If you leave your newer vehicle for any length of time, using one of these occasionally or leave it on while in storage. Makes a lot of sense. You will be rewarded with a car that is always ready to start and you will get longer battery life.

Since I leave all the MBs stored in the winter and it is cold here, I think this charger will pay for itself the first year of ownership.

Here are pictures of the eyelet wires install on my E320 CDI. They show the connection to the battery in trunk and the quick connect (I have a spare quart of oil and some growlers for brweries I might encounter going cross country):





Hope this is useful to other MB Diesel owners!

-- Chris

__________________
-- Chris

'95 E300, 216k miles, Silver Surfer
'05 E320 CDI, 138k miles
'07 S550 4matic, 69k miles

Gone but not forgotten:

'76 300D, 350k miles?, SOLD in 1995
'75 240D, 300k miles, SOLD in 1991