In the current campaign, the character is a level 5 battle smith artificer. I like to think of him as a novice inventor and had an idea for an infusion that would kind of reflect that. The infusion comes in the form of a device added to a weapon. At lower levels, the device tends to be a little unstable but as the Artificer levels up, they tweak and fine tune the device. I was hoping to gain some incite into whether or not this would be balanced. If not, maybe some suggestions on how to bring it up or down. The infusion would read as follows:

Item to be infused must be a melee weapon.

Max charges: 4

Once per turn, the user may expend a number of charges to add 1d8 lightning damage per charge to their next successful weapon attack. For each charge spent in a single successful attack beyond the first, the user takes 1d4 lightning damage per charge. If 3 or more charges are spent in a single turn, the infused device becomes damaged and must be repaired by the Artificer. The infused weapon regains 1d4 charges after a long rest.

At 10th level, the infusion no longer damages the user. 

Any thoughts and comments are appreciated,

Thank you