12 volt Sealed Lead Acid battery...aka deer feeder or alarm system battery. The main thing to look for is the amp hour rating. The reason the amp hour rating is important is because it determines how long your depthfinder will run on a single charge. Most depthfinders draw around 1/2 amp per hour of use, with newer multiple-function models drawing more. I would check the spec sheet for your depthfinder and find the unit's power draw. Then find a 12v SLA battery that will run long enough on a single charge to suit your needs. I use either a 7 or an 8 amp hour battery, depending on which one I've charged. My depthfinder draws 1/2 amp per hour, so a single charge gives me 16 hrs of continuous use on a fully charged 8 ah battery.
I can also power my submergible light with these batteries. They are great since they are leak-proof, waterproof, and lightweight. The 8 ah battery weighs around a pound or so.
I would also strongly recommend getting a battery charger with an automatic shut-off. These batteries will burst if overcharged.
Chris Bryant
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