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