Blueroomelectronics' question is still unanswered: We don't know what kind of battery we are talking about.
Some answers are about a 9v "transistor battery", which of course can not provide 80 W.
But a battery is a battery
And they come in lota of sizes and capacities.
A car's battery certainly can provide 80 W - Just leave your headlights on (while the motor is not running) and you have more than 100 W for some time - And then there are even bigger
batteries