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Bow Thruster Battery Banks: Can Lithium Ion batteries be used to power a bow or stern thruster?

Feb 20,2023 | TezePower

Regarding batteries used for a boat’s bow or stern thrusters: Most electrical engineers agree that a boat’s bow thrusters would ideally not be connected to the house bank of batteries and especially not when using Lithium-Ion Batteries that are protected 

  • Why is the case?
    Combining bow and stern thrusters on one battery or battery bank with the inverter and other electronics may not be a good idea because any spikes or peak voltages and current drawn from the thrusters could cause issues and possible damage to the connected electronics.
  • Also, when the thrusters are combined with the house loads to the house bank, the thrusters could empty the house bank, instead of the designated thruster battery bank.

Regarding potentially using Lithium-Ion batteries for a boat’s bow or stern thrusters:
Lithium-Ion batteries that have an internal BMS, will disconnect themselves from the circuit, in the case there are any issues that could potentially damage the batteries, this includes high amperage draws.

Each of our 100 Ah batteries can handle a 200 amp draw for only 3 seconds and 4 of them connected in parallel could handle 800 for 3 sec. However, once this threshold is met or exceeded, the BMS will disconnect the Lithium-Ion cells from the circuit, and cut off power to the thrusters, potentially leaving the boat in a precarious condition.
Also, we recommend a maximum continuous discharge current of 100 amps per 100 Ah Lithium-Ion battery. (400 amps per 4 batteries connected in parallel)
But this high of a current draw will drastically decrease the battery cycle life. Instead of potentially 6000 cycles, the batteries will be reduced to 2000 cycles or less.
Lithium Batteries as well as lead-acid batteries rely on total surface area of the metal to provide high current draws. Lithium-Ion batteries also come in different shapes and sizes. The 2 most common are the Cylindrical Cell and the Prismatic Cell.

The Cylindrical cells have less surface area and offer more amp hour/energy capacity but have lower current draw ratings, and the Prismatic cells have more surface area, but have less amp hour/energy capacity, and higher current draw ratings.
Our Lifeline Lithium batteries are built with cylindrical cells and therefore have less current draw ratings. The built-in BMS (Battery Management System) will shut off the discharge current if any potentially damaging thresholds are met.
Best Suggestion:
Use a separate battery or battery bank for the thrusters; without a Battery Management System that would disconnect the batteries from the circuit if any potentially damaging issues arose.