All memory chips store memory as 1's and 0's. One component used in electronic devices is a capacitor. Which is basically a temporary battery. It can be used to smooth out a signal such as AC/DC current or a frequency signal. This temporary battery can also be used to supply a minuscule amout of power to keep a microchips memory intact. So even if a battery is remove from a device, such as a portable radio with digital tuning, it will still retain the memory of the stations that were set by the owner. A microchip uses a very small minute amount of voltage to retain its memory because the settings are already in place. The voltage just has to hold them in that state. Where as creating memory in a new state requires much more power. However once set it is easily kept there. Think of it this way. If you have ever tried to push a car, you know the hardest part is to get it moving. Once it's moving though, very little energy/effort is required to keep it moving. It's the same with the memory chip. The capacitor is used to keep the memory in place. The battery power put it there.
Sorry to be so long winded but that's the best way I knew to describe it.