A long time ago, when building the boat, I was convinced that installing a bow thruster was going to pay dividends, primarily in tight docking situations in marinas. Looking back nearly 25 years, I realize now that the choices I made were dictated by circumstances and current technology. At the time, it was popular to install a 24V bow thruster, which practically forces you to also install a 24V windlass. At the time, I felt that I did not want a mixed 12V/24V electrical system in the boat, and also considered using hydraulic driven off the engine. However, this has drawbacks because the hydraulic power is noticeably less when the engine is just idling. Also, to get a 24V battery, you need to have a space in the bow to fit two big 8D size batteries, each weighing nearly 140 pounds.
So, as a compromise, I went with a single big 12V battery to drive both the windlass and the bow thruster. The bow thruster is a Wesmar T8E, with a 6HP 12V motor. This draws about 450A at 12V. The cables are heavy, and short. The windlass in an Ideal 12V V4C, which draws only about 120A. We actually bought our fifth bow battery a few months ago, at a cost of about 800 euros, and that prompted me to consider “can I make it better”. I realize now that the very high current demand of the bow thruster is probably responsible for shortening the life of that bow battery, which is currently specified at 1200CCA, 240Ah. It seems that we get 4-5 years at best out of a bow battery. With the single AGM battery, operating the bow thruster can pull the voltage down to 10.5V, with 460A, and that is bad for both battery health and the electric motor. So – what can I do at this point in order to make the bow thruster more effective, and make the battery last longer? Obviously, a simple answer (increase the system voltage to 24V and double the batteries) is difficult to achieve and expensive. I already have a 700Ah LiFePO4 battery in the house bank, and have been using LiFePO4 batteries since 2011. However, in my opinion, LiFePO4 batteries are not the best choice for this application because of the extremely high discharge current (450A) and the resultant expensive BMS and switching equipment. I considered “super capacitors” but these are better suited to applications of high current that only last for 1 or 2 seconds, not 15-30 seconds.
I instead chose to build and fit a Lithium Titanate Oxide (LTO) battery to power the 6HP bow thruster with charging from the existing 12V AGM battery via a Victron Orion XS 50A DC-DC charger. In my opinion, this is a highly effective solution due to the unique advantages of LTO technology tailored to the demands of a high-current, short-duration application like a bow thruster. LTO batteries excel in delivering exceptional power density and safety, capable of handling high discharge rates (up to 10-20C or higher, equating to 400A+ for this 40Ah LTO battery) without thermal runaway risks, making them ideal for the 450A draw of the thruster during brief, intense bursts (e.g., 10–30 seconds per maneuver). Their robust cycle life (20,000+ cycles) ensures long-term reliability, far surpassing AGM batteries, which degrade faster under high-current loads. Additionally, LTO batteries operate effectively across a wide temperature range (-35°C to +70°C), perfect for marine environments, and their low self-discharge rate (<2% per month) means the battery retains its ~13.8V storage voltage (~40%–50% SoC) after 6 months, ready for immediate use without significant capacity loss. This setup minimizes maintenance and ensures consistent performance for docking maneuvers.
I laid out my design using this simplified diagram, and set out to buy everything I needed while still in Cartagena Spain, and had easy access to online shopping.

After arriving at Tangiers Morocco, I started on the project by completely separating the windlass and bow thruster operations. The 8D AGM battery is now completely dedicated to driving the windlass. I laid out my LITOKALA 2.3V 40Ah cells in parallel, and started to charge them up to full capacity.

This took several days, and I had to charge some cells individually.

Then, I organized the cells into a cube, using preprinted black plastic end fittings and threaded rods.

There is no BMS, but I am using a HelTec 6S active cell balancer like this one, to keep the cells at the same voltage.

Charging the LTO battery from the existing 12V AGM battery leverages the current electrical infrastructure, avoiding costly upgrades while enhancing system efficiency. The Orion XS 50A charger, is now configured by bluetooth on my phone with a 15.0V absorption voltage, 14.4V float, and 13.8V storage. It efficiently tops up the LTO battery between thruster uses, restoring ~32–36Ah in ~30–40 minutes without overtaxing the 220Ah AGM battery (protected by a 12.3V lock-out and 50A input limit).

This integration maintains the AGM’s role as a stable power source, charged by the boat’s alternator and solar while the LTO battery handles the high-current demands, reducing strain on the AGM and extending its lifespan. The compact size and lightweight nature of LTO batteries compared to equivalent lead-acid options also save valuable space and weight at the bow. This combination delivers a reliable, safe, and long-lasting power solution for the bow thruster, optimized for both performance and compatibility with the existing system.
The installation required me to lay on the floor for some much enjoyed “boat yoga” while working in the hole.

I finished the installation a few days ago, and have done some testing. The existing AGM battery, now dedicated to running the windlass and “topping up” the LTO battery essentially stays at 13.2V while the LTO battery offers the muscle when operating the bow thruster. With a burst of 3 seconds, the LTO battery voltage drops from 14.6V to 12.6V, but then recovers to 14.6V in just as many seconds. With a burst of 5 seconds, the LTO battery drops from 14.6V to 12.0V, but then 5 seconds later has fully recovered again to 14.6V. In the meantime, the Victron DC-DC charger kicks in and takes current from the AGM to replenish the LTO. The AGM in turn is replenished by either the Volvo primary alternator, or solar spill-off from the house bank.
This is what the installation looks like, “inside the hole”.

Overall, I am very pleased with the results, effectively installing a purpose built dedicated battery for the bow thruster in the same physical space available – and one that is actually cheaper than an AGM option. Looking at the water churned up when the bow thruster is operating, our combined observation is that this improvement has made a noticeable difference. There are, of course, a few more switches and meters required to operate and observe this system, but I fitted those in a way that I think is very simple and easy to understand.







































































































































































