Originally Posted by OM617YOTA

Does your battery just meet 750cca, now? What temp is the battery at? My ~800 CCA battery did well over 1200 amps at ~70F, so if your battery is only testing at 750 amps at 70 deg or whatever the temp was, at zero it's going to have wayyyyyyyyyyyy less than specified. Obviously that doesn't answer whether it'll start your car, just food for thought.

Clamp on ammeters are inexpensive, maybe get one and see what it takes to start your car now? Factor in less output from battery at lower temps and double or whatever the current requirement to start your engine at cooler temps, might give you a somewhat educated guess, with some kind of data to look at.

If I remember come winter, I'll take a measurement on mine and see what it takes to start. Won't help you at all for multiple reasons, but now I'm curious.

Edit: Does the E300 have a particularly odd/expensive battery? Here in the PNW, I replace batteries every five years or so regardless of what condition they're in. On a six year old battery, I'd spend the $100 and replace it by the end of winter.