B&W 801-series 80 Q's?

Picked up a pair of 801 series 80's. Couple of questions?
1.) Can anybody think of why I shouldn't substitute a 9V lithium for the giant carbon/zinc that they came with? This is for the APOC circuit.
2.) I sold these back in the day - but I no longer remember what the two buttons on the front do/did? One has a diagram of a lightbulb on it - the one next to it has a diagram of a lightbulb with a slash mark thru it.
3.) The fuse on the back input plate is unlike anything I have ever run into before: It sorta looks like a adaptor to fit a "European" size fuse into a 3AG size holder. Why would anyone do this? Could the fusses in this adaptor be the solid silver fusses I've read about ? Anybody know what the standard type/ size and value of this fuse was ?
Appreciate the info.
Here's what I've learned:
1.) The batteries are available - about 16 bucks each. You can use a 9V "transistor" battery and a couple of alligator jumper clips to test the protection circuit. Still haven't been able to find a schematic of how this works.
2.) Without batteries - these things will work.Assume that without batteries - the protection circuit is inoperative?
The way this protection circuit works is that if you beat 'em to near death - the red LED will come on and the speakers will shut down -no sound.Quit being stupid ( turn it DOWN) and press the button with the lightbulb with a slash thru it -speaker will come back on and red LED goes out.The button with a lightbulb on it is the protection test button -press it and the red LED lights and no sound. Press the button with the lightbulb with a slash thru it and the red LED goes out and the speakers will make sound again.This is not the same system used in the subsequent APOC equipped speakers.The protection system probably explains why so many of these early 801's are still making music.
3.) Fuse is a 5A -again what it's hooked up to a mystery to me -can't find documents/schematic on these first generation 801's yet?
4.) Strangest thing about these speakers so far is the static impedance of these things measures in the 13-14 MegOhm range in one direction and around 3.5 MegOhm in the other.In other words - put your meter across the input terminals of these speakers with nothing going on and instead of measuring something in the say 4 to 16 ohm range you get MegOhms ???Sure would like to see a schematic of these series 80 speakers!