Following info and steps worked in my old lenovo
The bios zip file includes:
- 2 files .FL1(BIOS) and .FL2 (ECP: Embedded Controller Program / platform)
- executables with a name similar to winphlash (can be DOS or windows)
winphlash can backup current BIOS and apply a BIOS with extension .ROM and will not check for battery.
The .FL files have the format required by winphlash, so you can rename the extension FL1 to ROM or just force the filter to pick the FL file
I managed to Flash the FL1(BIOS) and it is recognized and works.
However I didn't know what to do with FL2 file, I tried to flash as i did with BIOS but I received a warning message saying that version and code is not the expected.
(update: ECP should always be flashed before than BIOS)
Anyway, despite the message I flashed the ECP/platform ROM and everything worked well.
BTW I don't consider buying a new battery the best solution.
Because in the practise not all people need a battery and for old laptops the cost can be similar to the laptop price.