J-Grow,
I had an old 12-Volt Marine Deep Cycle battery (the size of a standard car battery) that had been living (dying?) in my workshop for several years. I had charged it over night a few days before my first OAV (disaster) attempt. The next day I hooked up the OAV and timed how long the battery took to evaporate 2 TSP of OA. It took the battery 7 minutes, much longer than the 2 1/2 minutes folks say you should leave it in the hive.
On the day before my attempted OAV treatment, I put the battery on the charger, and then carried it out to the hives after dark. At the time I thought dark would be best because all the bees would be inside. After 7 minutes, I unplugged the vaporizer. 15 minutes later, I pulled the vaporizer out of the hive and let the bees out. The vaporizer still had a lot of OA sitting in the cup, so I knew my battery had died totally.
I drove my riding lawnmower out to the hive and hooked up to the battery. It's a smaller battery, but still 12 volts. I did the same time frame (7 minutes on, 15 minutes wait). During the 15 minute wait, I hooked the battery to the charger, and then repeated the process with my second hive.
After the second treatment, my lawnmower wouldn't start without another charge.
I was able to drive the lawnmower back into the workshop the next morning, but the three year old battery was never the same.
I bought a new car battery from Interstate battery, and haven't had any problems. I was able to treat both hives without a recharge, and 3 TSP of OA vaporizes in less than three minutes.
I've read from others that the vaporizer drains batteries pretty quickly, and so it is not advisable to count on using your car or tractor, as you may get stranded.
On Edit: I used a 1/4 teaspoon measure, not a 1 teaspoon measure. So, it was 1/2 teaspoon that was used when I had two boxes, and it was 3/4 teaspoon when I had three boxes.