Question

The total charge a household battery can supply is given in units of mA.hr. For example, a 9.0 V alkaline battery is rated 450 mA.hr, meaning that such a battery could supply a 1 mA current for 450 hr, a 2 mA current for 225 hr, etc. How much energy, in joules, is this battery capable of supplying?

Answer 1

Power = Energy / Time or

Energy = Power * Time

Power = I V (current * voltage)

Thus Energy = I * V * T

E = .001 Coul/sec * 9.0 Joules/Coul * 450 hr * 3600 sec/hr

E = 1.46E4 Joules

Note:

Q = .450 ma/hr = .45 coul/sec * 3600 sec = 1620 coul

E = V Q = 1620 coul * 9 Joules / coul = 1.46E4 Joules