" recharging " carbon batteries by heating them.

The heat makes the chemical reaction occur easier or faster. It doesn't really add charge to the battery. But if the battery tends to self-discharge, it speeds up that lossy effect.

You could get extra life out of the old zinc-carbon batteries by punching holes in the case and immersing in a sal ammoniac solution. When that wore out, you could still salvage some zinc and the carbon center electrode. Best to discard the black electrolyte.

I like your answer. You are right, my smoke detectors always ask for battery change in the middle of the night when it is cold. They never complain during the day.

Years ago, I noticed this phenomena, it took me a bit of time to think of the reason why.

Of course, once known, its completely obvious.....

Any dry cell/battery can be refreshed- no need to warm in oven as my father did 60 years ago(radio batts- expensive)- just use dc volts from higher source for short time only- eg 1.5v cell etc- hold in hand- 12v from car batt- will feel cell warming up in say 5 secs- while ever cell stays warm- equal to new cell- can repeat many times!. Yes, if left on refresh could explode!. Works with carb/zinc, alk,li-ion,li-po(all supposedly not be recharged!. A dedicated dry cell recharger works too- but these apply a stepped charge at a low rate so cell/ batt never heats up. The trouble with recharging cells/batts is that they won't hold the charge for long- but - Hey!- if you are out in the bush- will save you!. Cheers.

Beats me. Try asking this guy...