I have worked with many Thinkpad T30s; this is a problem with its CMOS battery. For some reason, they have a shorter lifespan than other systems. The T30 also allows you to set the time and date, but does not show an error message indicating anything wrong with the battery (usually).
http://www.impactcomputers.com/ibmpa...t30-parts.html will have the part you need.
To select the correct machine:
1. Your part number is on the bottom of the machine on a small black and white sticker "Type xxxx-xxx S/N ------------"... Where the first 4 x's are is your type number.
2. T30s were made with 2 resolutions shown below:
XGA - 1024 × 769
SXGA - 1280 × 1024
When the machine is running, right-click on the desktop and click Properties. Click the Settings tab and look at the resolution on the slider on the left. Attempt to slide it all the way to the right side. Whatever it displays is your maximum resolution.
Based on this information, select the correct model laptop (in Impact Computers) and click the "Power Supply" section. The part you need is called the "IBM Thinkpad Backup Battery". The image will likely look like a small battery wrapped in yellow plastic with a wire hanging out.