Panasonic Cordless Phones Manual Pnlc1023 ((new)) Link

Use only rechargeable Ni-MH AAA batteries . Alkaline or manganese batteries can cause the unit to overheat or leak, potentially damaging the base.

If the "Recharge battery" indicator flashes after less than 15 minutes of use, the batteries likely need replacement. Panasonic Cordless Phones Manual Pnlc1023

If the display is in a language you do not understand: Use only rechargeable Ni-MH AAA batteries