Choose the Best Fish Finder Battery

Fish finders are often used on kayaks and small one- or two-man boats and choosing right battery with maximum performance and minimum weight at acceptable price can be confusing thing to do.

Fish finders are often key elements for having a great fishing trip or coming home empty handed. Most common fish finders don't require large currents to operate, but the power supply must be constant and reliable.

On the larger vessels, when the main engines are off, fish finders are powered via boat's onboard battery (or batteries). On smaller boats, kayaks, pontoons or even inflatables, fish finders are often powered via dedicated batteries that must supply enough power for the fish finder to operate properly during fishing.

Powering fish finders, sonars, GPS and other electronics on larger fishing boats is not a problem - just plug the devices in and few Amps of current will hardly deplete the main deep cycle (dual purpose) marine battery, which is often connected to solar panels, wind turbine or at least, to the main engine's alternator.

However, when it comes to small fishing boats, pontoons, kayaks and even canoes, situation is not that simple.

Some of the best and most popular fish finder 12V AGM SLA or lithium 'drop-in' replacement batteries are given in the following table:

Brand/Battery Capacity Size (HxLxW) Weight Amazon Link
Chrome Battery 7 Ah 3.72x5.94x2.56 inches 4.1 pounds Chrome Battery 12V 7AH Battery
ExpertPower 7 Ah 3.70x5.94x2.56 inches 4.52 pounds ExpertPower 12V 7Ah Battery
Universal Power Group 7 Ah 3.86x5.94x2.56 inches 4.80 pounds UPG 12V 7Ah SLA Battery
Universal Power Group 8 Ah 3.94x5.94x2.56 inches 4.96 pounds UPG 12V 8Ah Battery With Charger
Universal Power Group 9 Ah 4.06x5.94x2.56 inches 5.17 pounds UPG 12V 9AH Battery With Charger
ExpertPower 12 Ah 3.9x5.94x3.86 inches 7.61 pounds ExpertPower 12V 12 Ah Battery
Mighty Max 12 Ah 4.00x5.94x3.88 inches 8.38 pounds Mighty Max 12V 12Ah Battery
EarthX ETX36C 12.4 Ah (1h) 5.9x3.4x4.5 inches 3.9 pounds EarthX ETX36C LiFePO4 Battery
Chrome Battery 15 Ah 3.74x5.94x3.86 inches 9.00 pounds Chrome Battery 12V 15Ah Battery
Mighty Max 15 Ah 3.95x5.94x3.89 inches 9.60 pounds Mighty Max 12V 15Ah Battery
PowerStar 15 Ah 6.6x7.13x3.00 inches 12.5 pounds PowerStar 12V 15Ah Battery
Universal Power Group 15 Ah 3.95x5.94x3.89 inches 9.60 pounds UPG 12V 15Ah Battery
Odyssey PC680 16 Ah 7.5 x 7.15 x 3 inches 15.4 pounds Odyssey PC680 Battery
ExpertPower 18 Ah 6.57x7.12x3.03 inches 11.68 pounds ExpertPower 12V 18 Ah Battery
Mighty Max ML18-12 18 Ah 6.57x7.13x3.01 inches 11.90 pounds Mighty Max 12V 18Ah Battery

Note: Amazon affiliate links open in the new windows, feel free to check the most current prices.

Of course, there are many more available 12V batteries in this capacity range, so choose according to your individual needs and preferences.

Required Battey Capacity

garmin striker mFirst step is to determine required capacity of the fish finder battery. Capacity is obtained by multiplying fish finder current (Amperes) and desired operating time (hours) and is given in Ampere-Hours (Ah).

Most fish finders consume around or less than 1 Amp of current, when powered from 12V sources. Smaller, portable models draw even less than that, but larger ones, especially fish finder/GPS combos can draw more than that.

For example, one of the most popular, compact and rather versatile fish finders Garmin Striker 4 GPS Fish Finder (Amazon link, opens in the new window), draws ~0.23 Amps, when being powered with 12V source.

Just to be sure, let us assume that our hypothetical fish finder draws 1.5 Amps at 12V.

When going fishing from kayak or similar small boats, fishing trips rarely last more than 10-12h and often are much shorter, for example 3-4 hours. Upon return to shore or larger boat, fish finder battery is recharged.

So, if one prefers longer trips lasting 10-12h, required theoretical battery capacity is 15 to 18Ah, while for shorter trips (3-4h), required theoretical capacity is 4.5 - 6 Ah.

In real life, battery capacity is lower than theoretical and hence, larger batteries must be used, depending mostly on the age and condition of the battery.

When buying new battery for fish finder, increase capacity by 20-25% - instead of 18Ah (theoretical) for longer trips, consider 21-24Ah batteries and instead of 6Ah batteries for shorter trips, consider 7-9Ah batteries.

And if you use smaller fish finder with lower power requirements, such batteries can operate much longer on a single charge.

Type of Battery

marine batteries 1There are several types of batteries which can be used for powering fish finders.

Sealed lead acid (SLA) batteries are commonly used as deep cycle or dual purpose marine batteries. They operate regardless of their position, they are leek proof, come in various sizes and shapes and they are rather cheap. Unfortunately, they are also the heaviest batteries used on boats and kayaks.

Good 7-9Ah/12V SLA (absorbed glass mat - AGM, or gel cell) battery weighs between 4-6 pounds (1.8-3 kg), while 18-21Ah/12V battery easily weighs 12-15 pounds (5.4-7 kg).

Personally, I would never recommend flooded lead-acid batteries for use on kayaks and small boats.

Nickel Cadmium (NiCd) batteries are lighter than SLA batteries, can provide insane high currents, but they are not environment friendly, have strong memory effect and other issues. If you need lighter batteries, choose Nickel Metal Hydride (NiMH) or lithium batteries.

Nickel Metal Hydride (NiMH) or lithium batteries provide same capacity for much lower weight. NiMH batteries can be up to 2-3 times lighter, while lithium batteries 3-6 times (or even more) lighter than SLA batteries of the same capacity.

However, such batteries also cost more money and usually require special chargers.

earthx etx36c mFor example, EarthX ETX36C LiFePO4 battery weighs only 3.9 pounds and is able to supply 0.23 Amps (for above mentioned Garmin Striker 4 GPS Fish Finder) for at least 53-54 hours(!) and 1.5 Amps for at least 8 hours. Also, such battery is protected by builtin Battery Management System (BMS) that also balances cells on a regular basis and can withstand at least 2000(!) slow discharge cycles down to 20% of initial charge. But, such battery also costs much more than similar AGM batteries.

Note: Lithium ion drop-in-replacement batteries are commonly designed as starting and as deep cycle batteries. Deep cycle lithium ion drop-in-replacement batteries can be used as excellent fish finder batteries, offering huge capacity with low weight penalty and can be charged with most SLA AGM battery chargers.

For example, Battle Born 100 Ah 12 Volt LiFePO4 Deep Cycle Battery features 100 Ah capacity and weighs 'only' 29 pounds - that is 3.45 Ah per pound of the battery.

Also, very popular ExpertPower 12 Ah 12V battery weighs 7.61 pounds (1.58 Ah per pound), and very sturdy and durable Odyssey PC680 (12V 16 Ah) battery weighs 15.4 pounds (1.04 Ah per pound).

Fish Finder Battery Box

marine battey power center mManufacturers of electric trolling motors like Minn Kota, Newport Vessels and similar, also manufacture battery box power centers. Such power centers are designed to be very robust, water- and dust proof, and resilient to mechanical damage.

Commonly, power centers accept BCI Group 24 and 27 batteries (60-100 Ah), and feature integrated circuit breakers, USB chargers, battery monitors, 12 V accessory ports and similar.

Although such battery power centers sound like an 'overkill' for fish finder batteries, they are highly recommended for any longer fishing trip, even when electric trolling motors are not used.

But, if you like to spend every possible free moment fishing from your kayak, put high quality battery in your power center box, connect small solar panel and/or small wind turbine and power your fish finder, GPS and even small electric trolling motor.

Note: All batteries should be protected from open water, sun, cold wind etc. Store them in the watertight compartment, low in the boat (to improve stability, especially if you choose larger AGM SLA battery).

Charging Fish Finder Batteries

battery charger small mBatteries should be charged using chargers designed for specific battery type. Using wrong chargers can lead to damaged and destroyed batteries and chargers and even to injuries or worse due to possible heat, fire, smoke and even explosion. And we are serious about this.

SLA batteries are cheap and can be fully charged overnight or even faster, using 'fast' chargers. Note that such fast charging tend to slightly reduce battery's lifetime. Using 'fast' chargers, NiMH and lithium batteries can be charged even under hour, although charging them for 4-6 hours prolongs their operating lifetime.

Again - using wrong chargers can lead to physical damage and injuries caused by high temperature, smoke, fire, explosion ...

Long story short - if you are not sure what to do, go for cheap and reliable AGM SLA battery, dimensioned for your fish finder. Even 2-3 small, 7Ah/12V batteries with proper charger, cost under $100. Over time, you will figure out your most common practices and you will be able to more accurately define your needs regarding fish finder batteries.