Hey Auto Doc . did not say it was correct , I just said "ponder"Hi Ozcub,
That is an "old wives' tale" that has been around since the early wooden encased battery days. That story has been disproven countless times.
The more important safety factor would be if a battery is "gassing" it is expelling a very explosive hydrogen gas. This happens quickly when people set a charger on too high of a setting.