Hi Jack, Cool story about the trucks :) Shorting an extremely cold battery is probably not as scary as a room-temperature one, since they internal resistance would be much higher when it is so cold, I think. I think the effect I was describing is just called the "reversible heat effect." Reversible in the sense that when you discharge, you re-absorb some of the heat you generated during charge. Sean On Sun, Dec 13, 2009 at 1:01 PM, John Gardner wrote: >> for lead acid, slow discharges actually COOL the battery a little below ambient... > > Very interesting, Sean. Is there a name for this effect? > > IIRC there was a procedure for starting military 2-1/2 Ton trucks > in extreme cold which involved shorting the battery for a few > seconds, circa 1970. > > I never did that, but others claimed to have done so. It > does get cold on the DMZ in Korea... My MO was to take the > battery inside the hootch, which also makes it somewhat harder > to steal. > > In the morning build a small fire under the vehicle, thaw it out, re- > install the battery, and you're good to go. > > This is a somewhat heroic proposition with a deuce-and-1/2. The > battery is a two man carry... > > Jack > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist