Talktime or talk time is a term used in the wireless voice communications device industry to describe the duration of constant two-way conversation supported by a device's single fully charged battery.
In cellular mobile telephony, talktime is highly dependent on the network environment such as the distance to the closest cell tower as base stations demand increased handset transmission power when signal strength wanes. Moving fast while talking (as in a vehicle) also negatively affects talktime.
Manufacturers measure talktime in controlled conditions and the quoted numbers are rarely reached in real-life scenarios.
References
Talktime Wikipedia(Text) CC BY-SA