I have seen hotter batt give far more voltage under load than one that has cooled down, but I don't think that artificially heating them would do the same.
Here we agree my friend. It's not the heat, but the "allowed to cool down" part. Batteries have peak performance when used immediately after being fully charged. It's not that they are hot, that is a side-effect (and a bad one) of being fully charged. If you cool them WHILE they are being charged, they will perform just as well, but they will have longer life.
If you don't pay for your batteries, then this is not really an issue...