Choosing a battery for an electric outboard sounds simple.
The motor runs on a 72V system, so you buy a 72V battery.
Right?
Not necessarily.
The Momentum M10 is a high-performance 10kW electric outboard, designed to deliver an exceptional power-to-weight ratio for high-speed tenders, sailboats and applications that demand strong torque. To get that performance, the motor needs more than a battery with “72V” printed on the case.
It needs a battery whose actual operating voltage, chemistry, current capability and usable capacity match the motor.
That is why we created the new Momentum M10 Electric Outboard Battery Calculator.
Try the Electric Outboard Battery Calculator
Why We Built an Electric Outboard Battery Calculator
The M10 was designed to pair with our MB-6 6.4kWh battery, giving owners a matched, plug-and-play propulsion system.
But many M10 owners also choose third-party batteries.
Some want larger fixed battery banks for extended cruising. Some already have a battery they would like to use. Others have found an inexpensive 72V LiFePO4 or golf-cart battery and want to know whether it is suitable.
The problem is that “72V” describes a voltage class, not a complete battery specification.
A 20S NMC battery, a 20S LiFePO4 battery and a 24S LiFePO4 battery can all appear in the broad 72V category while behaving very differently when connected to the same electric outboard.
That difference can affect how much of the battery you can actually use.
Rated Battery Capacity Is Not Always Usable Battery Capacity
This is one of the most important concepts behind the calculator.
Imagine two batteries that are both advertised as 6.4kWh.
At first glance, they appear equivalent.
But if one battery reaches the M10’s minimum operating voltage while a significant amount of energy still remains inside the pack, the motor cannot make practical use of all 6.4kWh.
That unused portion is what we call stranded energy.
This is particularly relevant to some inexpensive 20S LiFePO4 72V golf-cart batteries.
A typical 20S LiFePO4 battery is approximately 73V fully charged and only 64V nominal. The standard M10 minimum operating voltage is also 64V.
Depending on the cells, load, voltage sag and battery configuration, only around 60 to 75% of the battery’s rated capacity may fall within the M10’s standard usable voltage range.
A battery that looks inexpensive based on its advertised kWh can therefore become much less attractive when you compare its cost per usable kWh.
The calculator makes that difference visible.
More Than a Simple Battery Runtime Calculator
Most battery calculators start with the capacity printed on the battery and calculate how long a motor can run.
That is useful, but it assumes the motor can access all of the energy you entered.
The Momentum calculator first asks a more important question:
Can the M10 actually use that battery’s energy?
The calculator checks the pack against the M10’s electrical operating window and estimates the amount of battery capacity that is genuinely available to the motor. It currently supports presets for the MB-6, 24S LiFePO4, 22S LiFePO4 and 20S LiFePO4, as well as custom battery configurations. Momentum Electric Marine USA
From there, it calculates several things that are particularly useful when comparing batteries.
Voltage Compatibility
The calculator checks the battery’s full-charge voltage against the M10’s maximum input voltage and compares the lower part of the battery’s discharge range with the motor’s 64V standard minimum or optional 60V configuration. Momentum Electric Marine USA
This immediately helps identify battery configurations that look compatible based on a nominal “72V” label but are poorly matched electrically.
Usable Capacity vs. Rated Capacity
Rather than assuming every advertised kilowatt-hour is available, the calculator estimates how much battery capacity can actually be used by the M10.
That makes comparisons between different chemistries much more meaningful.
A 6.4kWh battery with 95% usable capacity is a very different proposition from a 6.4kWh battery where only 65% is realistically available.
Stranded Energy
The calculator also shows the battery energy that remains below the motor’s usable voltage range.
This is one of the most useful features when evaluating lower-cost 72V batteries because it exposes something that rarely appears on a battery seller’s specification sheet.
You can see not only how much battery you are buying, but how much of it your M10 can actually use.
Voltage Sag Under Load
Battery voltage is not static.
When a high-power motor draws current, battery voltage falls under load. The amount of sag varies with the battery chemistry, cells, state of charge and current demand.
The calculator accounts for voltage sag when estimating usable battery capacity rather than relying only on resting battery voltage.
That is particularly important with a 10kW electric outboard capable of substantial current draw.
Runtime and Illustrative Range
Once the calculator determines the energy available to the motor, it can estimate runtime at different power levels and provide an illustrative range profile for a light tender.
These figures are estimates, not promises of how far a particular boat will travel. Hull design, weight, wind, current, sea conditions and operating speed all affect actual range.
For detailed boat-specific range modelling, other tools on the market focus heavily on hull resistance and operating speed. WattSailor, for example, models boat characteristics and plots estimated range based on how the boat is used.
Our calculator is designed to answer a different question first:
Is the battery itself a good electrical match for the M10?
Compare MB-6, LiFePO4 and Custom 72V Batteries Before You Buy
One of the easiest ways to use the calculator is simply to switch between the preset battery configurations.
Compare the Momentum MB-6, a 24S LiFePO4 pack, a 22S LiFePO4 pack and a 20S LiFePO4 pack.
You can immediately see how chemistry and series count change the battery’s voltage range, usable energy and estimated runtime.
If you already have a battery in mind, select Custom and enter its specifications.
This makes the calculator useful whether you are choosing between commercially available batteries, designing a larger fixed battery bank or simply trying to understand whether an inexpensive 72V battery is really the bargain it appears to be.
UI showing caution and explanation
Why the MB-6 Remains the Simple Option
Third-party batteries can be excellent solutions, particularly when you need substantially more capacity or a custom installation.
But there is also value in simplicity.
The Momentum MB-6 was designed specifically for the M10. Its battery chemistry, operating voltage, BMS, charging system and monitoring are already matched to the motor.
It is plug and play.
There is no need to determine whether the chemistry, series count and operating voltage are appropriate or integrate a collection of individual components into a complete propulsion battery system.
That does not automatically make the MB-6 the right answer for every installation.
It does mean that when comparing it with a lower-priced third-party battery, you should compare usable energy and the complete installed system, rather than simply comparing the price printed beside two batteries with similar advertised capacities.
Try the Free M10 Battery Calculator
If you are considering a third-party battery for your Momentum M10, run the numbers before you buy.
The calculator is free and does not require registration.
Try the M10 Electric Outboard Battery Calculator
Check your battery’s voltage compatibility, estimate its usable capacity, see how much energy may be stranded below the motor’s operating range, and compare expected runtime before committing to a battery system.
If you are considering a custom battery and are unsure about the results, send us the battery specifications. Momentum can help confirm whether its basic voltage range and current capability are suitable for the M10. The calculator page currently offers this configuration sanity check at no charge.
A battery should not just say 72V. It should be the right 72V battery for the motor you are asking it to power.
