Lenovo issued a recall of certain batteries shipped with some Thinkpads between November 2005 and February 2007, notably including the T60.
More information is posted on the [Lenovo web site].
Some details from that page:
On March 1, 2007, Lenovo voluntarily recalled approximately 205,000 9-cell lithium-ion batteries. These batteries were manufactured for use withThinkPad notebook computers that shipped worldwide between November 2005 and February 2007.
Lenovo sold the batteries with new notebook computers or as optional or replacement batteries on the models listed below.
* ThinkPad R60 and R60e Series
* ThinkPad T60 and T60p Series
* ThinkPad Z60m, Z61e, Z61m, and Z61p Series
These models may have shipped with either 6-cell or 9-cell batteries; only the 9-cell batteries with the part number FRU P/N **92P1131** are being recalled.
[See the above website for instructions on verifying the part number of your battery.]
Until a replacement for a recalled battery arrives, if you intend to transport your ThinkPad notebook PC or use it in a manner that may subject it to a strong external impact, you should turn off the system, remove the battery, and only power your ThinkPad by plugging in the AC adapter and power cord.