Talktime is usually measured in hours for any rechargeable communications device (mobile phone

Mobile phone

A mobile phone is a device which can make and receive telephone calls over a radio link whilst moving around a wide geographic area. It does so by connecting to a cellular network provided by a mobile network operator...

 or cordless phone).

This is the maximum expected duration a fully charged battery

Battery (electricity)

An electrical battery is one or more electrochemical cells that convert stored chemical energy into electrical energy. Since the invention of the first battery in 1800 by Alessandro Volta and especially since the technically improved Daniell cell in 1836, batteries have become a common power...

 is expected to last under perfect conditions (ambient temperature

Temperature

Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...

 has a major impact on battery life).

A safe rule of thumb is to use the following guide to expected talktimes as your phone battery ages (the last column has a specific example of 12 hours talktime):

Age	fraction of max	percentage est.	talktime
under 1 year	3/4	75–85%	9–10 hours
1–2 years	2/3	66–75%	8–9 hours
2–3 years	1/2	50–66%	6–8 hour
3–4 years	1/3	33–50%	4–6 hours
over 4 years	1/4	25–33%	3–4 hours

Most phone batteries don't last more than 4–5 years and have to be replaced by then.

Talktime is different from the standby time of the device, which is always much longer.