I drive a Ford Fiesta 1.4l diesel, a much smaller vehicle than most of our American and Canadian cousins drive.

In the recent cold spells here in UK (down to -15 / -20degC)I left the battery on trickle charge when parked up at home - around 1 to 1.5 Amps. Whilst my neighbours would struggle (and often not succeed in starting their engines) mine always started first time.

Apart from keeping the battery topped up I imagine there would be a very small amount of heat generated in the battery helping to keep it from chilling too much.

My own rule of thumb is that once a lead-acid battery is more than 2-3 years old it's on borrowed time. There's MUCH more to it of course, but imagine the corrosive effect of immersing lumps of metal into a bath of acid...you've got yourself the beginnings of a battery!

Very interesting to read about the various heaters you use over there. If our cold winters are to continue we're going to have to go down the same route as you.

Thanks for the really interesting discussion.

JJ