I bet it's much easier to borrow a battery from another, similar laptop, such as:
Lenovo ThinkPad Edge 14" 15" E420 E520 E40 E50 L410 L420 L510 L520 SL410 SL510 T410 T420 T520 Series Laptop.
Using
any broken motherboard from a T60/T61/R60/R61/X60/X61/T400/T500 and newer Thinkpad and
any dead battery for one of those, I made my own
battery extension cord, by cutting out the battery connectors from such a dead mobo and such a dead battery, and soldering them together, using a length of 7-wire cable (cut out of an old IDE cable from a PC).
This lets me use ANY shape battery in ANY shape laptop that uses the same 7-pin battery connectors.
You could also try and find a T60 interposer card P/N 41W1130 and cut its connector in half and extend that (as above).
It's the leftmost black piece on this picture:
