Cockney Steve,
Interesting and valuable information - the kind of detail about aircraft systems that a pilot might learn by reading....... The flight manual for the aircraft!
How else would they know for certain what type of battery was installed, or alternator vs generator? Or, as BPF correctly mentioned, the proper selection of the battery master for the use of ground power!
Sure, there are some with oodles of experience with aircraft, who pretty well have some flight manuals memorized, and the aircraft systems equally so, but others are new, and need the resource. The regulations cannot tell who is who, so everyone is required to carry the flight manual - just in case!
If a placard is missing, and the pilot should know what it said, before it was scraped off by the passing bag, he could read the limitations section of the flight manual, and there it will be! I once nearly killed myself for not knowing the information on a placard, which had not been installed on a Cessna 303 I was flying - but it was in the flight manual - literally in fact, in a zip bag, stapled to the revised limitations page! The revised checklist also stated the newly prohibited operation - I wish I had read it before I tried it!
I watched a Mooney pilot/owner loose the skin from his knuckles, when attempting an emergency gear extension - you gotta pull that gear motor breaker before you turn the hand crank, or a few turns in, the motor will suddenly drive it, and as it comes around - Ouch!
I like flight manuals and checklists - and the skin on my knuckles!