Meantime, back on the farm, I found an older, failed battery that was undoubtedly in the machine when manufactured in 1996. Popped it in the freezer (Google "freezer trick + NiMh") for a day. Took out and left to warm up and dry off. After a couple of failure notices and subsequent resets (eMates are known for this on replacing batteries), it took a full charge. Huzzah. Gotta love those NiMh cells.

But I still think I am going to order me one or two (I have two eMates) of these. No fuse -- I asked -- but from what I've read here, a fuse is probably not really needed. I couldn't buy a pack of 4 NiMh AA cells at WallMart for as little.

It is worth looking at this guy's listings, btw, as there are other assembled battery configurations available that would be suitable for modest adaptation in 540c/190/Duo/5300 battery packs.