Battery Bridger for Items that for example use 3x 9V Batteries, and you want it to run with only 2x 9V Batteries.

You can just use and old 9V Battery connector and connect both end together and glue it on top of the case.
This is perfect if the batteries are connected in serial and you want to reduce the Voltage by 9V.
For example if you use 3x 9V Batteries, you'll be using 27V. If you only want to use 18V you can just use 2 normal batteries and 1 of those battery bridgers. Like this the circuit will be closed and work aswell but with less Voltage.