I have used a standard Sealed Lead Acid battery for several years to power my fish finder without issue, however these batteries do have one downside.... they are heavy! Lithium batteries offer a much lighter option but lightweight comes at a cost, and lithium batteries must be fully waterproofed to use safely on the water. This is how i made a Lithium battery with waterproof housing for my kayak...
Lightweight Power Source for Kayak Fish Finders
There is a solution.... Lithium.
Not only is Lithium a great song by grunge rockers Nirvana, it is also number 3 on the periodic table of elements. It is a highly reactive alkali metal with a wide number of applications including use in rechargeable battery cells. Lithium-based batteries are used widely in modern electronics. Your phone will have one, so will your laptop and various other mobile devices. There are several types of Lithium batteries available, including Lithium Polymer (LiPo) and Lithium-Ion (Li-Ion). Lithium batteries are great.... they are lightweight and they hold a lot of charge for their size. So why are they not widely used on fishing kayaks?
Safety Concerns and Disadvantages of Lithium Batteries
- Overcharging - if the battery is continually charged then the excess charge will have no where to go and dissipate as heat, potentially leading to failure and combustion of the lithium cells within the battery.
- Short Circuiting - this is where current is allowed to travel between the positive and negative terminals of the battery through a low-resistance conductor. In this scenario the battery starts to pump current back into itself almost unrestricted and with no where for the current to go it will rapidly heat up leading to failure and combustion of the lithium cells. Short circuiting can occur when the battery is wet, particularly in saltwater, and this is a realistic possibility within the confines of a kayak.
Overcharging or short circuiting a lithium battery must therefore be avoided at all costs. Luckily high-quality modern lithium batteries come in robust sealed housings and have integrated fail-safe features to minimise the risk of battery failure. A good quality charger will prevent overcharging. Housing a battery within a waterproof box will further prevent the possibility of short circuiting a lithium battery on a kayak.
You can even buy 'off-the-shelf' lithium battery packs for kayak fishing from companies such as Nocqua and FPV but none are readily available in the UK and have to be sourced from the US or Australia. Ah well... i'll make my own!
Sourcing a Lithium Battery for Kayaks
The Aliant YLP battery range uses safe Lithium iron phosphate technology with embedded 'Active Balancing' electronics control microprocessor unit to minimise risk of battery failure. The specifications were good too, with the battery performing well in both hot and cold temperatures, with up to 3000 charge/discharge cycles, low self-discharge rate when disconnected, fast recharging, no liquids or lead and it can be mounted in any position. The battery is all housed within a tough ABS shell with chunky well-separated terminals to connect wiring too.
There are various sizes in the range and i settled on the YLP10 which has a charge hold approximately equivalent to that of a 10Ah SLA. According to Aliant it weighs in at just 740g with a size of 114mm x 69mm x 90mm! compact and lightweight... perfect!
Making a Waterproof Box for a Lithium Iron Phosphate Battery
- Aliant YLP10 Lithium Iron Phosphate Battery
- Oxford Oximiser 3X Advanced Battery Management Charger
- Lock and Lock 1.9L Waterproof Box (HPL818)
- Index Marine Bulgin 2-Pin Socket with Cap
- Index Marine Bulgin 2-Pin Plug with Cap
- 2 x AMP Superseal 1-Way Waterproof Electrical Connectors for 0.5-1.5mm wires
- 4 x M3 x 8mm A4 Stainless Steel Bolts
- 4 x M3 A4 Stainless Steel Nyloc Nuts
- 4 x M3 A4 Stainless Steel Washers
- 1 x Ring Terminal Crimp Connector - Red
- 1 x Ring Terminal Crimp Connector - Blue
- A length of twin-core electrical cable - i used approx 40cm.
- Block of high-density closed-cell foam
- Drill with various size drill bits
- 22mm Hole Saw Bit
- Small Flathead Screwdrivers
- Small Allen Key
- Small Spanner
- Crimping / Wire-cutting Pliers
- Wire Stripping tool
Making a Waterproof Battery Box
Wiring in the Lithium Battery
Take a short length of twin core wire and carefully remove the outer black sheath with a blade or scissors, leaving the red and black wires seperated. Strip back approx 6mm of wire at each end of each section.
Fitting the Waterproof Plug to my Fish Finder
Place the wire into the screw-down terminals on the plug and tighten up. Make sure you connect the wires to the correct pins to correspond to the equivalent terminal on the socket - positive to positive, negative to negative. The plug also features a notch so that it can only be plugged into the socket in the correct orientation.
Charging a Lithium Iron Phosphate Battery
- Motorcycle mode for batteries under 36Ah - trickle charging at 0.8A and 14.4V
- Car mode for batteries up to 125Ah - charging at 3.6A and 14.4V
- Winter mode for cold charging and AGM battery charging - charging at 3.6A and 14.4V
The motorcycle 0.8A 'trickle' mode will be ample for charging the small Aliant YLP10 battery - although the battery itself does state that the max charge current that can be used is 10A, so for faster charging the car 3.6A mode could be used. As the YLP10 holds the equivalent charge to a 10Ah Lead Acid battery, i'll stick with using the motorcycle mode for batteries up to 36Ah. Another point to note is that Lithium batteries can be damaged if continually trickle charged i.e. never disconnected from the charger and continuously charged as it's discharged with use. As i will be disconnecting the battery once charged, discharging the battery during use and then re-charging the battery there should be no issue.
The charger automatically checks the polarity of the battery connection before charging to prevent cross-charging the battery. The charger also analyses the condition of the battery as either 'weak' or 'strong'. The charger provides a 'soft-start' to carefully recover deeply discharged batteries, and then offers a 'bulk fast charge' to quickly charge to 85% capacity and then an 'absorption charge' to bring the battery to a full 100% charge. Once the battery is charged the charger will gently maintain the battery at full charge until it is disconnected. All the info is displayed on an backlit LCD display for ease of use. Its not a cheap charger though but i managed to pick one up for around £60 online which i didn't think was all that bad.
The charger comes with a couple of leads - one with ring terminals for permanent attachment to a battery or one with clips for easy attachment and removal from battery terminals, and this would be the one i would be using. It also comes with a wall mount holder too.
Sealed Lead Acid Vs Lithium LiFePo4 Battery Box
Testing on the water
Lightweight and compact, the lithium battery box easily fits inside the 8in hatch on my Hobie Revolution 16, however i choose to keep it in the bow hatch as there is a little more room there. With the lithium-ion cells housed within the sealed ABS battery casing and the battery housed within my DIY waterproof battery box, there is minimal risk of battery failure and/or short circuiting as a result of contact with water. The battery box is further protected by being placed within the hull of the kayak which is at worse damp and is unlikely to present a submersion scenario to the battery box. I feel confident that the lithium battery cells are suitably protected and the battery safe to use on my kayak.