glenbrook:
I would like to believe that, but I am not sure that plan B is all that simple.
Maybe you are right, perhaps they have a non-Lithium-ion replacement that will fit the slot. But if they do, it is going to be 4 times heavier and twice the volume
Do I incorrectly recall that the battery weighs some 65 lbs? Adding another 200 lbs doesn't seem significant. (Guessing that the APU battery was identical to the Main for spares commonality, I've not multiplied by two.)
I do think that lithium batteries do have other advantages e.g. low internal resistance that might make replacing them more than simply a weight-and-volume issue, though.