Hi rafach!
Welcome to the forums!
Can you tell us under what conditions the battery gets warm/hot? Is it during the charging cycle only, or normal use as well? Is this a battery that came with the machine (stock) or was it purchased as a separate item?
It is normal (to a certain extent) that a battery will heat up significantly while charging. If the heat issue occurs only during charging, it would be worthwhile inspecting the power supply (including the contacts) for any possible sign of failure. If the power supply is failing, then it's possible that it's charging the battery at a much faster rate, thus causing overheating.
It is possible, however, that the battery cells may be deteriorating. If you have the Power Management software installed, there's a feature to verify the condition of the battery, the number of charge cycles, etc. Also, visually inspect the condition of the battery, the terminals for any outward signs of problems (look for green/gray matter on the battery terminals, bulging, etc). Depending on your findings, it may be necessary to replace the battery.
Having said this, Lenovo did issue a recall on batteries that were supplied with certain machines. If you suspect that something may not be right, and to put your mind at ease you can always check here ---> Lenovo Battery Recall Notice
Steve
