Noun
undervoltage (countable and uncountable, plural undervoltages)
A voltage that is too low.
The battery can still be charged while "bucking" an overvoltage, but while "boosting" an undervoltage, the transformer output is too low to charge the batteries. Source: Internet
This type of UPS is able to tolerate continuous undervoltage brownouts and overvoltage surges without consuming the limited reserve battery power. Source: Internet