dock fish finder/ battery?

The wife is leasing a large slip for her ski boat. Slip is in 25+feet of water and I have been catching crappie there pretty regular. Decided to cut a crappie door in the slip floor and will drop a bamboo brush pile soon. I want to mount a fish finder and transducer on the dock side wall near the crappie door above the brush pile. Probably going to go used on ebay, Lowrance. Anyone have any idea how small a battery I can use? Really don't want to mess with a big deep cycle marine battery like I have on my boat. The smaller the better. I want to be able to take the battery with me and charge it at home. Thanks in advance.

MIGHTY MAX ML7-12 12-Volt 7.2 Ah is $17.50 at Lowes and is rechargeable. I'd try that before buying a lithium.

Google kayak fish finder battery

Thanks, will do!

I use one like the version Chickenman recommended on my kayak with a Lowrance 7" Ti2 and get good service with it. I can generally fish for at least 2 days, sometimes 3 before needing to recharge it.