un·der·charge 
(ŭn′dər-chärj)
(ŭn′dər-chärj)tr.v. un·der·charged, un·der·charg·ing, un·der·charg·es
1. To charge (a customer, for example) less than is customary or required.
2. To load (a firearm) with an insufficient charge.
n. (ŭndər-chärj′)
An insufficient or improper charge.