From the Showdown Troller manual:
12 Volt Rechargeable Battery Option
The Troller unit can also be powered by using 12V rechargeable battery (not
included). The power / transducer cord that comes with the Troller unit is
equipped with a 12V “pig-tail” lead that can be attached to an optional accessory,
the Showdown Troller Performance Pack. Once your Showdown Troller
unit has been secured to the Performance pack, you will be able to operate
the unit using 12V power. The Troller unit can be placed in and removed from
the performance pack with ease by using the Quick-Slide bracket that comes
with the performance pack. You do not need to have the AA batteries in place
for the 12v battery to power your Troller. Whenever your Troller is hooked up
to the 12v battery, no drain is being put on your AA batteries.