Good god...what all are you powering?
I guess those Margarita blenders pull more than I thought.
Ok, heres what I have and havent had any problems in 2yrs so far.
I have a 5 amp hr battery...much like what you find in security systems or computer battery backups. (internet price was like $12bucks)
Weighs maybe 5 pounds...prolly less really.
I keep it in a pelican drybox with a waterproof plug (west marine) dangling through a drilled hole so I can plug the fishinder in.
I put a zip tie LOOSELY around the sail post and then use a metal clip on the handle of the battery box and clip it to the zip tie.
The batery rests on the floor of the yak but stays where I put it via the clip and zip tie.
I use a Humminbird 728 and that gives me somewhere about 38hrs of use.
Way more than my butt can take sitting down honestly.
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Don't lead me to temptation, I already know the way.
Syn