I had a Pokemon that had the ability.Traded it and forgot what volt absorb does.
If you get hit with an electric type move, the attack does no damage and heals HP.
A Pokemon with Volt Absorb heals 1⁄4 of its maximum HP when hit by an Electric-type attack.
My Source - http://pokemondb.net/ability/volt-absorb
http://bulbapedia.bulbagarden.net/wiki/Volt_Absorb_(ability)
When a Pokémon with Volt Absorb is hit by an Electric-type move, its HP is restored by one quarter of its maximum HP, and the move will have no effect. This includes the effect of activating a Cell Battery. In Generation III, Thunder Wave is unaffected by Volt Absorb.
BTW: Fun fact! Volt absorb is only an ability on six electric type Pokemon!