Panasonic KX-TGP600G Operating Instructions Manual page 19

Ni-MH batteries can also self-discharge. This self-discharge depends on the ambient
temperature. At temperatures under 0 ℃ (32 ℉), the self-discharge will be the lowest.
High humidity and high temperatures support the self-discharge. Also long-term storage
will lead to self-discharge.
CAUTION
RISK OF EXPLOSION IF BATTERIES ARE REPLACED BY AN INCORRECT TYPE.
DISPOSE OF USED BATTERIES ACCORDING TO THE INSTRUCTIONS.
1.11 Battery Information (KX-TPA60 only)
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