Benjamin Franklin's Lightning Musket

I am thinking  about a prequel for the Western campaign I am going to run. It would be based on my own world but use concepts from the Colonial Gothic setting and 3.5e rules for compatibility with my other campaigns. Magic would exist but practitioners stay mostly hidden because of the Salem Witch Trials, the Inquisition, etc. The party would be mostly spies, saboteurs, and troubleshooters in the employ of the Continental Army or the Sons of Liberty. There would be some Steampunk-esque inventions running around but these would be one-of-a-kind items and only rarely encountered. 

One example of this technology would be Benjamin Franklin's Lightning Musket.

This weapon is made of stout red oak and reinforced with brass fittings. When the trigger is pulled a forked bolt of lightning erupts from the weapons twin barrels. The bolt has a range of 150' but is wildly inaccurate, incurring a -4 penalty to attack rolls. The weapon is powered by a battery that sits on top of the weapon (where the scope would eventually be mounted on weapons in the future). The power output is controlled by a dial located directly behind the barrels. It can be adjusted to release a set amount of energy with each shot (ranging from a minimum of 2d6 up to a maximum of 10d6). The battery holds 10 charges and each fie of damage costs one charge to be expended. Changing a battery is a full-round action that provokes an attack of opportunity. 

• On a Natural "1", the weapon backfires. Every creature in a 10' radius suffers 1d6 damage/charge left in the battery (save for half) and the weapon cannot be used again until it is repaired. 

• The battery is recharged by flying a kite in a lightning storm (gaining 1 charge per die of damage the lightningwould inflict on a target). Lightning strikes are channeled down the kite string (actually thin copper wires) into a battery holder. This holder has slots for up to six batteries to be charged (when first battery is full, leftover lightning begins charging the next battery in line). If all batteries are full, excess energy is discharged into the earth via a grounding wire.

 

Example picture - scope is where the battery would be, the cylinder in the middle is the power setting.