There are more parameters to batteries than just voltage. There's also current, energy, and power.
CURRENT: The Amp-hours which is how many ampheres the battery can supply for one hour before dying. Voltage is not taken into account so this can only be used to compare batteries of the same voltage.
ENERGY: The Watt-hours is the same thing as Amp-hours except voltage has been taken into account so this can be used to compare batteries of different voltages.
POWER: Then there is the power the battery can provide. Like above, this can written as the maximum current you can draw from the battery, or you can take voltage into account and write it as the peak Watts the battery can supply.
It is possible to get a battery that can provide a lot of energy, but you can only pull that energy from the battery slowly (i.e. low power). Such a battery can be used to power a low power load for an exceedingly long time, such that it might even provide more total energy than a high power load that runs for a shorter amount of time. However, it cannot power this high power load since you cannot pull energy from the battery fast enough to provide the power this load requires.