Is it true that the higher the power of the attack, the more HP the Pokemon with the ability gains?
e.g:Thunder heals more than Spark and Hydro Pump heals more than Bubblebeam.
Volt Absorb and Water absorb heal a set amount of HP, 1/4 or 25%. So it doesn't matter wether you were hit by Thunderbolt or Thunder, it will always heal 25%.
Source 1 and source 2.
This is not true,the ability heals the holder of the ability 25% of its max HP.
Source:Knowledge and this and this.