The battery life was under 1 hour.  Step 1 was eliminating the battery.

The inside was just a 200mAh battery & bog simple board,  Sadly, the 5 minute timer was burned in the chip with no RC circuit anywhere.  An outboard microcontroller could drop kick it every 5 minutes.  It frequently stutters when water drops build up around the transducer & cover it, so a 5 minute drop kick wouldn't be noticeable.

The transformer makes 120V p-p on 1 pin if the input voltage is 5V.  The other pin is connected to B+.  The output voltage drops to 110V p-p if the input voltage is 4.2V.  The lion kingdom wanted to reduce the chance of burning out when it runs out of water so tried to drop the input voltage with a diode.

USB power could use a bit of capacitance to keep it from browning out.  The next problem is expanding the reservoir.  The easiest solution is seen as drilling out the top & fitting 2 pipes.  1 pipe allows water to be pumped in from a water bottle.  A 2nd pipe lets air escape.  The tank needs a water level sensor.  It's expensive & hard to pump water.  The 1st task is finding out how long the transducer lasts.