06 E320 CDI. Both batteries replaced by PO at dealer 3.5 years ago. Charging system in good working order.

As it's gotten colder, I would periodically get the "convenience features temporarily unavailable"....no big deal.

Three days ago, drove 140 highway miles and let car sit for three days. Tested main battery and it was only reading 700 CCA. So I figure battery is marginal at best and should probably be replaced.

Start the car and get the red visit workshop battery message. That usually points to a bad aux battery from what I understand. But since the main battery was pretty weak I thought that the likely culprit.

Ran a scan and was told the the aux battery was bad. Measured voltage and it's under 10v. So I figure at least that one's bad.

My question: could a bad aux battery prevent the main battery from charging properly? Or should I simply conclude that both batteries are bad?

I'm happy to throw a couple of AGMs in there and be done with it. But I am curious if perhaps the main battery may have significant life left.

__________________
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, 142k mi, wastegate conversion

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

Mine did all kinds of crazy stuff before I replaced the Aux battery.

I bought a new main battery from the dealership thinking that was the real issue but it still gave me all the same convenience functions temporarily unavailable and visit battery workshop errors on really cold mornings.

My understanding was the Aux battery is only there for the SBC if you lose power, but I could be wrong, even so, my experience above mirrors yours.

On the main battery on my wholesale account, the battery was cheaper from the dealer than from Napa.

However the Aux battery is hilariously expensive, I bought it online for like $29, been in since April and no more battery warnings.

__________________
68 280SL - 70 280SL - 70 300SEL 3.5 - 72 350SL - 72 280SEL 4.5 - 72 220 - 72 220D - 73 450SL - 84 230GE - 87 200TD - 90 190E 2.0 - 03 G500

Nissan GTR - Nissan Skyline GTS25T - Toyota GTFour - Rover Mini - Toyota Land Cruiser HJ60 - Cadillac Eldorado - BMW E30 - BMW 135i

That's a great price on the aux battery...I paid about $80 with discount at Advance Auto.

__________________
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, 142k mi, wastegate conversion

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

The main battery is rated at 760A using the EN standard. So I really should have been measuring using that standard anyway. When I do that, it reads 680, which is OK.

__________________
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, 142k mi, wastegate conversion

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

I just solved my red battery message problem. From my research, 4 things can cause that message usually. Bad main batt, bad aux batt, bad BCM, or bad alternator.


I checked both my batteries, both north of 12v disconnected. Alt was reading 13.8 or so at all times, so I concluded bad BCM. My local indy happened to have a used BCM that I swapped in, still the red message of death.


Replaced the alternator with rebuilt AC Delco (didn't feel like paying twice as much for rebuilt Bosch). Red msg has been gone now for 700 miles.


Moral of the story, even with alternator reading healthy on scangauge, you can have a bad alternator.


I've never had a more difficult time changing an alternator...drain coolant, remove radiator fan, remove two water hoses to get the alternator out the top. No room to get it out the bottom. very un-Mercedes-like.


David, in your case I'm guessing just the SBC battery is bad (assuming cranking is strong).

__________________
Mark in MA
05 MB E320CDI 402k Granite Grey Metallic
05 MB E320CDI 267k Black
05 MB E320CDI 232k White
05 MB E320CDI 209k Tectite Grey
99 Dodge 2500 Cummins 5sp 148k
62 Jeep CJ-6 120k

I wonder if I should replace the voltage regulator just for good measure....original at 169k miles.

__________________
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, 142k mi, wastegate conversion

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

Shertex, I was getting "convenience features temporarily unavailable" it turned out to be main battery. I got a Sears Gold AGM, for less then $100 on Sale last winter.

__________________
06 MB E320 CDI 123k miles
14 Sienna (wife's DD) 36k miles
11 GL350 Bluetec 136k (Sold)
96 E300; 292k+ miles (Donated)
11 Sprinter 22K+ miles (Sold)

Replaced the aux battery and everything seems to be working fine. Was able to charge main battery to 95% capacity. Voltage while driving is a stable 14.3 volts. But I'll keep on eye on it. It is the original alternator, after all.

__________________
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, 142k mi, wastegate conversion

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

Does anyone know if it is OK to drive around with a bad Aux battery in these W211s at least temporarily? I'm getting the visit workshop warning and suspect the SBC battery has gone bad since car starts fine.

Thoughts?

__________________
-- 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