Well I pulled the trigger and bought a PirahnaMax 165, a basic no frill unit.

Thanks for link MP. I ordered a 10 AA battery holder after reading that 10 give you much longer battery life than 8.

I also bought 12 Panasonic Eneloop Lithuim batteries and a nice charger.

I was in Radio Shack getting some stuff for my power pack build and noticed they have battery holders for 6 AA's.

That made me wonder IF it would be worth it to use 2 x 6 AA holders wired in series as a power source?

I have the extra 2 batteries anyway, but am I thinking wrong about IF 10 is better than 8, 12 would be better than 10?

Unit draws 100 mA ( no backlight).
Humminbird says between 10-20 volts, so with 18, I'd be under that, but is there any benefit from doing it?