Lenovo ThinkPad T420i - Manual (Page 8)

Batteries
DANGER
Personal computers manufactured by Lenovo contain a coin cell battery
to provide power to the system clock. In addition, many mobile products,
such as notebook computers, utilize a rechargeable battery pack to
provide system power when in portable mode. Batteries supplied by
Lenovo for use with your product have been tested for compatibility and
should only be replaced with approved parts.
This system does not support batteries that are not genuine Lenovo-made
or authorized. The system will continue to boot, but may not charge
unauthorized batteries. Attention: Lenovo has no responsibility for
the performance or safety of unauthorized batteries, and provides no
warranties for failures or damage arising out of their use.
Never attempt to open or service any battery. Do not crush, puncture, or
incinerate batteries or short circuit the metal contacts. Do not expose the
battery to water or other liquids. Only recharge the battery pack strictly
according to instructions included in the product documentation.
Battery abuse or mishandling can cause the battery to overheat, which can
cause gasses or flame to “vent” from the battery pack or coin cell. If your
battery is damaged, or if you notice any discharge from your battery or the
buildup of foreign materials on the battery leads, stop using the battery
and obtain a replacement from the battery manufacturer.
Batteries can degrade when they are left unused for long periods of
time. For some rechargeable batteries (particularly Lithium Ion batteries),
leaving a battery unused in a discharged state could increase the risk of a
battery short circuit, which could shorten the life of the battery and can
also pose a safety hazard. Do not let rechargeable Lithium-Ion batteries
completely discharge or store these batteries in a discharged state.
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Safety and Warranty Guide