reliable laptop battery vendors?

[Seth Gordon]

My employer recently gave away some hardware it didn’t need any more, 
and I helped myself to a free ThinkPad T43.  The only problem with the 
machine is that the battery is non-functional; I can leave it plugged in 
all night, but as soon as the power cord is bumped, the screen goes black.

Googling “t43 replacement battery” turns up a bunch of hits, all from 
vendors I’ve never heard of.  Who can I trust?