What is battery size / group code for 300m ???

Correct. Which means that batteries last much longer in cold climates
than in hot climates, but people erroneously get the impression that
cold weather does them in because the final failure *usually* shows up
on a blistering-cold night. In a hot climate, the battery can show up
dead as a post any time of year and often without the slightest warning.

I give more credit to the comparatively cool (though painful to get at)
location on that vehicle. That location has to knock at least 50 degrees
F off the average temperature of the battery compared to putting it up
in the top of the engine compartment as usual.

 

When its -20F out, I wouldn't be going out to start the car anyway. I'd
be loading the truck to move south...

When I was in Seattle (Keyport/Poulsbo/Bremerton, actually) last year,
it seemed to be old car heaven in general. I've never seen so many older
vehicles in daily use. The one that took the prize was a (formerly)
white '69 Charger covered in green moss and tree sap humming happily
down the road. It passed me in about the same spot several days in a
row. Same for a circa-1955 International pickup truck- except it was a
little (ok, a lot) cleaner.

 

Heat, vibration and deep-cycling kills batteries.

In summer you have heat.

In winter you have deep cycling, and you have way more vibration if
you drive on hard-packed snow that doesn't get cleared, and you also
have more pot holes.

You generally also have more use of electrical accessories in winter
(glass defoggers, seat heaters, etc) and more use of headlights
(because of reduced daylight in the winter). All that extra use
promotes deep cycling.

I've already replaced my front sway bar bushings once, and they need
to be done again. That tells you how much vibration I've experienced
in 8 years of driving my 300M.

I live in a climate where the daytime temp doesn't go above 40f for 4
months of the year. I doubt that's the primary reason my battery has
lasted 8.3 years.