What is the memory effect?

Rechargeable batteries do actually have what is commonly referred to as a memory. If a battery is consistently used at only partial capacity, the crystal structure of the inner chemicals will physically change, altering the capabilities of the battery. In essence, if you consistently use 25% of a batteries charge, it will change to only offer you 25% of its original charge.

For radio control batteries used in cars, running your vehicle until the charge is used up may not be so difficult. But if you use these radio control batteries in airplanes, draining the battery all the way down in your plane can obviously be disastrous.

Finally, lithium polymer batteries like those above never develop the dreaded memory effect and coupled with their light weight they are perhaps the ideal RC batteries availalbe today!