I’m experimenting with upgrading my boat’s bow thruster by switching from AGM to lithium batteries to shorten wire runs. The Side Shift brand thruster, externally mounted at the bow, originally used two AGM starter batteries with a 20-foot wire run to the relay, which reduced efficiency.
Disclaimer: I’m not a marine technician, just an end user. This is entirely experimental by me, and I’m taking the risk. This post/video is not to be taken as instructional. Copying me may be dangerous and void warranties. You have been warned!
Initially, on dry land, I installed/tested a 460 amp-hour Vatrer lithium battery near the thruster. However, the over 3,000-watt motor draw I measured once in water neared the battery’s continuous draw limit. So, I’ve repurposed it as a house bank and have instead paralleled two 280Ah WattCycle batteries at the bow. They can output a combined 400 amps continuous draw and are capable of surging up to 1,200 amps. They fit in the bow install location well and better meet the thruster’s high surge current demands.
For safety, I added a two-way switch to toggle between the lithium setup and the original AGM system, ensuring a fallback option. The system is protected by a 400-amp ANL fuse and 300-amp terminal fuses with an AIC rating (Ampere Interrupting Capacity) of 10,000 amps. However, I’m considering a class T fuse (AIC 20,000 amps) for better lithium compatibility per American Boat and Yacht Council (ABYC) recommendation. The WattCycle’s built-in BMS (battery management system) also has over-current protection and over-temperature protection as an added safety feature.
Also, I replaced corroded thruster wires and fixed wireless controller interference by relocating it away from the relay. The setup has worked flawlessly for over a month, delivering more vigorous thrust than the old AGM system. A 30-amp DC-to-DC charger (set to 10 amps) tops off the batteries underway, and a 30-amp shore power charger handles larger needs.
The upgrade has significantly improved maneuverability in tight marinas, with the lithium batteries’ high capacity and minimal voltage sag ensuring consistent power. The windlass also operates smoothly, benefiting from shorter wire runs and high surge capacity. I’m evaluating the thruster’s motor compatibility with lithium’s higher voltage (13.2 volts versus 12.8 volts for AGM, plus the usual sag under heavy load) and plan to consult the manufacturer. Overall, the system’s enhanced performance has been appreciated.
Bowthuster LiFePO4 Power System Mods Explanation Video
Product Links:
- Side Shift Bow Thrusters
- WattCycle Website
- Wattcycle Amazon
- Blue Sea 400A ANL Fuse
- ANL Fuse Holder
- Blue Sea MRBF Block
- Blue Sea 300A MRBF Fuse
- Blue Sea Battery Switch
- TopDon 30A Battery Charger
- SRNE 30A DC-DC Charger
