How long does a D battery last?

Answer 1

That depends on the current drawn from it. Standard D cells are rated between about 10,000 mAH to 15,000 mAH. Therefore a load drawing 100 mA from a D cell should give a lifetime of somewhere between 100 hours to 150 hours. More current shorter life, less current longer life.
No set answer to that, it depends on the power consumption of whatever they're connected to.

Answer 2

Duracell lasts as long as Eveready, Rayovac lasts about twice as long as those two, and Energizer lasts over twice as long as Rayovac, but at a steep price. For 15$, you can buy 4 energizer or 12 Rayovac. Unless you are powering some sort of lifesaving equipment, I'd buy a load of Rayovacs and switch them twice.

Answer 3

It will be good to at least the date marked on the battery, which is based on predicted shelf life (i.e. life if not used). But exact prediction of the life of a battery is difficult.

The life of any battery will be significantly extended if stored in the refrigerator (but DO NOT freeze).

Answer 4

A typical D battery can deliver about 12 amps for one hour.
A typical D Cell can provide 12,000 mAhours.

A ma is 1/1000 of an amp

Answer 5

They are 1.5 volts, and I think 150 mA.