I found that for some MicroVAXen, such as my 4000-300,
there is a Panasonic
cordless phone battery that almost exactly fits where the original TOY battery
does, and the connector is the same! I've mentioned it here on CC, so the part
number should be in the archives.
Yes, I have done something similar. Here in the UK Maplin sells these, although they are
relatively expensive.
Regards
Rob