I believe you me 50 Kilo Watt Hour. 3Watts is a good ballpark answers for most laptops or you can check the manufacturer site for the standby watts usage. HP is 2.3 watts in standby so a 50KWH battery would last for 50,000 / 2.3 is about 21,000 hours. Due to other facts such as heat and the chemical composition though they can lose that charge much faster. Even removing the battery from the device it will still eventually completely discharge.