In the first Futurama movie "Bender's Big Score", Bender travels back in time to ancient Egypt in order to steal gold and other expensive valuables from pharaoahs. A few seconds later, Bender is seen walking into the room with the treasure that he has stolen. Clearly, he has gone back in time at least one millenium, but in the episode "Obsoletely Fabulous", he needs an alcohol recharge within mere days. How is it that Bender can survive for thousands of years, presumably underground similar to his experience in "Roswell that Ends Well", without an alcohol recharge while still able to keep time in his internal clock to arrive back into the room at the perfect moment from whence he just recently departed?
In "Roswell that Ends well" Bender only had use of his head. And couldn't use the rest of his body because he was decapitated. So Bender only needed to use a fraction of his power to ensure that his head is on.
For Bender's Big Score, Bender could have just slept everything off. If that weren't the case, Bender does keep a lot of Alcohol inside his storage unit. If that weren't enough he could also take some from his paradox copies.
The way computers work is that they even calculate time when they are off. Not keeping track when they are off, but adding time slept to the time that they were currently off. Say one computer was off for 3 hours at 2 PM. The computer, when it wakes up, would calculate the time it slept (3 Hours) and adding it to the time before (2 PM). Or something like that, I'm not sure but I think it's like that. Corret me if I'm wrong.
Alcohol quantity and amount of power needed determines the energy needed. Bender, an Alcoholic, is lazy, therefore he doesn't need to charge his fuel cells that often(He doesn't consume that much power, or use that much energy). But when he does "work", he still fuels up even though he doesn't need to.