After being written to, the insulator traps electrons on the FG, locking it into the 0 state. However, in order to change that bit, the insulator has to be "overcharged" to erase any charge already stored in it. This requires higher voltage, about 10 volts, much more than a battery can provide. Flash systems include a "charge pump" that slowly builds up power and releases it at higher voltage. This process is not only slow, but degrades the insulators. For this reason flash has a limited number of writes before the device will no longer operate effectively.