Thanks for all the replies. Just to answer some of the comments. The battery was new and correctly maintained, albeit in order to save weight, the company had fitted a light weight battery which obviously did not have as much grunt as the usual larger one. To lose both generators in a 76 would be highly unlikely in which case you couldn't do an ILZ anyway, especially where we operated as there wasn't one. Conditions were bright blue vmc although quite warm about 35 C. If the battery didn't like the charge rate, and of course the 76 has no ammeter, voltmeter, loadmeter,etc just an amber light ( like a 1930 Austin 7!), then the battery hot system should come into play if things overheat.
