There's a bit more to adding a forced induction system such as a leaf blower. My first concern would be the fact that the motor in the blower is probably not rated as a "continuous duty motor" . Occasionally using it to blow leaves out of the driveway is one thing. The other item would be the injection tuning for the extra air to have correct air/fuel ratio. Normally the fuel delivery is done solely by how much air is flowing by the mass airflow sensor. This is why you can't "flood" out an engine by suddenly stomping on the gas at low RPM. Unlike a downdraft carburetor that can dump loads of raw gas without enough air and ends up choking on it and dies. Now with that being said, can the injection system deliver enough fuel for the amount of air you'll be feeding it? You may need some high flow rate injectors. You'll need a good tuner that allows you to make adjustments to the injection rates. Also this may be an option, if they have a tuner that allows you to custom program different stages you could leave one stock and stage two for example would be when you turn on the blower. This would make it last longer, then when you need the extra boost you turn on the blower and switch to stage two program. With that type of operation you could just as well use the rechargeable battery the blower came with and just recharge it when needed. You can wire in parallel two or three packs to get more run time. That's where you connect the positives together from each battery and the negatives from each together then take your power from the positives and the negatives you tied together. This will double or triple your total capacity but the voltage will stay at 18 volts. DC to DC conversion at the amount of current to run a blower motor may get expensive and complicated. One other way, however, not very efficient, would be to use an inverter circuit boosting the voltage into AC then rectifying it back into DC with an 18 volt regulator. Then the other item would be a variable speed device maybe working with the throttle position. Which could be a variable resistor (potentiometer) attached to the gas pedal mechanism. Or if you can make use of the electronic throttle systems they use with no mechanical connection to the engine. Those might be optical shaft encoders to determine how far the pedal is depressed. Then it can get a bit complicated converting pulses to a variable speed control circuit of the type used in cordless power tools. Which are high current MOSFET. Basically high power switching transistors. You also need to keep in mind that there's a possibility of destroying an engine beyond recognition! That's why exhaust driven turbo chargers have waste gates to vent off excessive boost pressure, like after hauling ass and the turbo is spooled up at who knows what RPM and you let off on the gas. That turbo is still pumping a massive amount of boost air that you don't need going to the engine. You can end up with very violent backfiring in the intake system. Sometimes leads to catastrophic damage, like a turbo blowing apart into shrapnel.