It seems to vary dramatically....on my diesels I'd be lucky to get 6-7 years from a battery with our harsh winters....but on my 2001 E320 I just replaced the ORIGINAL battery in January because it was cranking very slow if I left it in the cold for more than a couple days. Battery was roughly 18 years old. Pretty incredible. Original MB/Varta battery. Put in a Duracell AGM and its been great.

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

Interesting that we have had to replace our E320 battery fairly often. Maybe 4-5 yrs.

One problem we have, is too many cars! Or cars we don't ever drive very far.

Originally our E320 sat a lot in summer and was mainly used for long trips in winter. The electronics drain the battery while sitting. Then we might go for short drive and park the car again. Repeat this and battery is sitting there at a low state of charge which is not good for a battery. Car now gets driven much more, but we have same situation with our current newer go-south car. I now use a smart battery maintainer on seldom used car.

My old 300D gets drive a lot in summer, but always very short trips. Each start drains the battery a bit and then trip is not enough to recharge it back to where it was. By end of summer, I notice engine barely turning over before it starts. Overnight charge restores it!

So as barry said - driving car regularly leads to longer battery life (so long as you drive it far enough to recharge amount drained at start) Probably because battery is always almost fully charged.

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

The same seller has listed more of the CTEK 7002s at $75:

CTEK 7002 Battery Charger/maintainer and power source -- $75

I'm using one of these on my E320 CDI and S550 4-matic over the winter here in OH....if I get a few more years of battery life on each, it will pay for itself. I can also install a new battery and it will maintain power so settings stay static during the change.

__________________
-- 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

Still three left:

CTEK 7002 Battery Charger/maintainer and power source -- $75

__________________
-- 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