It's normal with rechargeable batteries, when charging your IBM Thinkpad t40 series notebook battery for the first time that charging is complete after just 10 or 15 minutes. Just simply remove the IBM Thinkpad t40 series battery from the laptop and repeat the charging procedure.
Try To avoid over-charging, especially, do not let your laptop battery over discharge. It is normal for IBM Thinkpad t40 series notebook battery to become warm when charge and use you battery. The battery exhaust much faster under the high temperature, you should avoid using your laptop battery in shady, cool place. Hit the battery, and other acts will also accelerate depletion of battery. So, pay attention to your battery as much as possible.
If you don't use your IBM ThinkPad T40 battery laptop batteries for 1 month or longer, you should remove the battery from your notebook, make sure leave your battery power about 40%, stored in a shade, cool, dry place away from heat, metal objects and direct sunlight, but not in the refrigerator. It’s objected strongly store your IBM Thinkpad t40 series laptop battery for over three months without any using. A charged IBM laptop battery will eventually loses its charge if unused. It may therefore be necessary to recharge the battery after a storage period.