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

I bought 2 of the smaller 0.8 amp CTEK's https://www.amazon.com/gp/product/B006CQ9BMO/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1 Jan 2016 @ $35 each. Today, the same charger is $20 more @ $55 each! That's a 57% increase in less tha 3 years!

The 0.8 amp unit works fine to maintain the biggest H8 or group49 batteries for our diesels. The bigger 4.3 amp unit is not necessary for what you are using it for. The only advantage it has is that it will bring a depleted battery up to full charge faster.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Yes, I wanted to be able to charge a depleted battery as well. I would spend the extra $8 or so and get the MUS 4.3 model that can charge as well as maintain.

__________________
-- 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

I found out the hard way that the AGM batteries do not like to be idle, such as in storage. Not only that, they will go completely, as in zero, flat and it's virtually impossible to revive them.

So, if your vehicle sees extended periods of non-use, I would recommend going with the standard lead-acid battery. It's much more forgiving of this type of treatment. Of course, staying "plugged in" is an alternative.

__________________
Sam

84 300SD 350K+ miles ( Blue Belle )

Unfortunately if you have an interior battery it has to be an AGM for safety reasons.

__________________
The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

The 0.8 Amp CTEK will also charge a depleted battery, it just takes longer than the 4.3 Amp unit. If I have to quick charge a depleted battery, which is seldom, I have a 20 Amp non smart charger which will do it faster.

Per user reviews of the CTEK MUS 4.3 Amp model, it gets too hot to the touch when charging a depleted battery. Is that true from your experience? That would concern me.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

The newer MB's require AGM batteries so lead acid battery may not be optimal solution. I agree they seem to run down fast when not in use.

__________________
-- 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

The 0.8 model is not rated for our battery size (95 Ah) for charging per CTEK's manual and would not comply with California's energy efficiency standard either (meaning it uses too much energy for the amount of charge it delivers...your electric bill will be higher then if using other models). It is only rated for charging 1.2–32 Ah batteries.

The cases on the CTEKs 4.3 does get warm but not "too hot to the touch". I would suggest leaving any charger out in open with plenty of air circulation. Electronics don't like excessive heat anyway so better air circulation is always better.

__________________
-- 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

While my 1.25A charger has always worked fine, it does take quite a while....there are times when it's taken a good 15 hours or so to reach a fully charged state. I wonder how much faster the 4.3A CTEK would be.

__________________
14 E250 Bluetec 4Matic "Sinclair", Palladium Silver on Black, 154k miles
06 E320 CDI "Rutherford", Black on Tan, 172k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver on Tan, 142k mi, wastegate conversion, ALDA delete

19 Honda CR-V EX 61k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife

I have two chargers that I use.

Compact 2A that I leave plugged into our E320 for winter:
MotoMaster Eliminator Intelligent Battery Charger, 2A | Canadian Tire (similar to CTEK)


The larger one is sold as a marine charger, but is really just an automotive smart 10A/15A charger. Very light plastic body (doesn't rust like the two older metal bodied chargers that I still have)

MotoMaster Nautilus Battery Charger,15/10/2A | Canadian Tire

Current sale prices are about what I paid for my chargers 5+ years ago. C$105 for both (US$80)

Not always happy with Canadian Tire, but these chargers work well.

They also carry the Noco range. Around here, CTEK now seems to be sold at Princess Auto (our HF) and not at good prices it seems.

__________________
Graham
85 300D,72 350SL, 98 E320, Outback 2.5

I understand. Maybe a secured and externally vented compartment lined with absorbent material. Of course, then you get into the cost of building such a thing.

__________________
Sam

84 300SD 350K+ miles ( Blue Belle )

The E320 cdi I have came with a lead acid battery from the dealer. The electronics never liked it. It may be that the newer MBs are designed to run with AGM batteries specifically.

__________________
-- 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

The 4.3 does get pretty warm to the touch when it is in its "full charge" state (light #4 or the red circle indicator) on a severely low battery but not during the other stages. The unit is designed as a maintainer, not as a charger. Its proper use is for AGM batteries not lead acid types.

I like it because it has a "DE-sulfinator" mode. Might just be propaganda hype or coincidence but it worked on a couple of old batteries I had given up on.

__________________
“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
― Brian P. Cleary, You Oughta Know By Now

Can you provide a link where it states the 0.8 amp model "does not comply with California's energy efficiency standard", whatever that really means?

In a week or 2, I am going to measure my 0.8 amp CTEK unit's idle current using a (Kill-A-Watt) which is maintaining 2 large diesel batteries connected in parallel which should be currently fully charged. I will also feel if it is warm, hot or cool to the touch. That will give me a real world indication of energy efficiency of the 0.8 amp unit.

Do you have a Kill-A-Watt electricity usage monitor to check the real world efficiency of your 4.3 amp unit?

Here's the spec of the 0.8 amp unit:
US 0.8 PART NO. 56≠ 865
The US 0.8 ofers state of the art technology and is perfect for charging
smaller 12V batteries that can be found in scooters, motorcycles, jet skis,
snowmobiles, ATVí s and lawnmowers. It is also suitable for maintenance
charging ën ormal sizeí car batteries. The unique display allows the user
to follow the entire charging process. The US 0.8 is designed to protect
vehicle electronics. It is non≠ sparking, reverse polarity protected and
short≠ circuit proof.
ï Charges batteries up to 32Ah. Maintains larger batteries up to 100Ah.
ï Fully automatic, 6 step charging process includes patented
desulphation and pulse maintenance programs.
ï Compact tough design ñ splash resistant and dustproof to
IP65 standards.
TECHNICAL DATA
Voltage 14.4V
Charging current Max 0.8A
Charger type 6 step, fully automatic charging cycle
Battery type 12V lead≠ acid batteries
Battery capacity 1.2ñ 32Ah, maintenance charging up to 100Ah
Insulation IP65 (splash and dust proof)
Warranty 5 Year Limited Warranty



Here's the spec of the 4.3 amp unit:
MUS 4.3 TEST&CHARGE PART NO. 56≠ 959
The MUS 4.3 TEST&CHARGE combines an advanced microprocessor
controlled battery charger with a battery and alternator test function
to provide the ultimate in battery testing, charging and maintenance.
TESTING ñ Three easy to use programs to test battery voltage, start≠
ing power and alternator performance to provide a complete picture
of battery and vehicle charging system health.
CHARGING ñ MUS 4.3 TEST&CHARGE provides excellent charging
performance. The charger solves a broad range of battery problems
and features include a patented automatic desulphation program
and a special reconditioning function that revives and restores
deeply discharged and stratifi ed batteries. The patented Float/Pulse
maintenance makes the charger ideal for long≠ term maintenance.
TECHNICAL DATA
Voltage 14.4/14.7/15.8V
Charging current Max 4.3A
Charger type 8 step, fully automatic charging cycle 3 voltage test programs
Battery type 12V lead≠ acid batteries
Battery capacity 1.2ñ 110Ah, maintenance charging up to 160Ah
Insulation IP65 (splash and dust proof)
Warranty 5 Year Limited Warranty

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Per CTEK's product guide https://smartercharger.com/wp-content/uploads/2018/03/CTEK-Product-Guide.pdf the MUS 4.3 and my US 0.8 unit are for lead acid batteries. Which one do you have that is for AGM?

The MUS 4.3 unit has 3 voltage output levels of 14.4/14.7/15.8V, while my US 0.8 unit has just one @ 14.4V. The 15.8V is what allows it to charge at the higher current of 4.3 amps and is the reason why it can get very hot when charging at max current. The 0.8 amp unit will just be warm charging at its max of 0.8 amp given both units appears to have the same size package.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked