ThinkPad R40 not charging battery (2723)

Well if it's not the battery then I would imagine it is the power supply...I would try getting a new one and trying that.

if the r40 is the same as the t40/t41/t42/t43

the yellow charging port has a copper connector inside it

over time with use the copper connector gets pushed in and loses it flexibility so doesnt come out far enough to make contact

to test if this is the problem get a small piece of cardboard or fold paper

put it in the charging port

then put the charger in

and no i am not winding you up and no it wont go on fire or anything

the bit of card/paper is just enough to move the pin on your charger over the tiny bit it needs to contact the bit of copper i

mentioned earlier

if it charges like that then the charge port is the problem--if not as suggested try a new charger--cheap on ebay even for original ibm ones

if the yellow port bit of copper is the issue--you can either try to hook it with a small bit of metal with a bend on the end and pull it out a bit

or replace the charging socket--they arent soldered on those ibms