The talk time you get on a single charge all depends on the type of rechargeable batteries used. I already replaced my batteries in my Panasonic handsets after several years of use.
The original batteries gave about 1000 charge/discharge cycles before I needed to replace them. That means you should get up to five years before needing to replace the batteries.
I am now using two AAA 1.2-volt nickel metal hydride (NiMH) rechargeable batteries rated at 800 mAh each in my Panasonic phone handsets. NiMH give more talk time than NiCad batteries, but may have a slightly shorter lifespan.
I can easily talk for three hours on a single charge. I have also left the phone off the charger for several days without using it. The standby time is several days if left off the charger.
It’s important to understand that battery efficiency is dependent on the temperature of the room. It’s best within a range of 50°F to 86°F (10°C to 30°C). In addition, if your phone is left in temperatures above 104°F (40°C), the charging process can be affected, and the batteries can deteriorate and damage the phone.