Electric outboards are expensive, and a significant portion of that cost is the lithium battery that powers the outboard itself. These batteries usually make up about 35-45% of the total cost of a portable outboard and even more for non-portable systems. If you plan to keep your electric propulsion system for a long time, you'll need to replace your battery well before you need a new electric outboard.
In this guide, we'll explain how lithium batteries age and the steps you can take to ensure that your battery lasts as long as possible.Â
Lithium batteries degrade over time, which means that as time goes on, their maximum capacity decreases (just like your phone's battery). The speed of this degradation is primarily impacted by three things: calendar aging, cycle aging, and how well you take care of it.Â
Degradation from calendar aging of a lithium battery refers to capacity loss due to the passage of time, regardless of use.Â
Degradation from cycle aging of a lithium battery refers to capacity loss from charge / discharge cycles.
You don't have any control over the calendar age of your electric outboard's battery, and you probably don't want to try to extend its life by minimizing the number of charge / discharge cycles; that would defeat the purpose of buying it!Â
But how well you take care of the battery is very much within your control, and in this guide, we'll explain how to do so. Following these basic principles will help your battery last as long as possible and perform the way you'd expect.
Useful life is the period during which a battery can still perform its intended function adequately. The industry standard threshold (depending on who you ask) is when capacity drops to 70-80% of original rated capacity — at that point it's considered past its useful life for most applications. The battery will still work, but you'll have significantly less range compared to when the battery was new. Most batteries for electric outboards have a useful life of 7-12 years.
Before we jump in, there are a few definitions and concepts that are important to understand.
State of charge (SOC) is the level of charge of your battery.
Whether your battery is relaxed or stressed depends on your SOC. When your electric outboard's battery is under 20% SOC or over 80% SOC, it's stressed. Between 20% and 80%, it's relaxed. The more time your battery spends relaxed, the longer it will last.
Ghost drain or self discharge refers to how lithium batteries lose charge over time while they're sitting around and not in use. The speed of ghost drain depends on a few things, but typically it's about 1-3% per month.
Deep discharge is when your battery's SOC gets so low that it cannot be charged with an off the shelf charger, only on a cell by cell level. For large, expensive batteries like the Torqeedo Power 48-5000, you may be able to have a service center recover your battery. Batteries for portable electric outboards under ~5hp typically cannot be recovered if they become deeply discharged.
Deep discharge typically happens over the winter when a battery is stored for more than three months and has a low SOC to begin with. Read our guide on electric outboard battery winter storage to learn more.
Quick Answer: What can I do to ensure that my electric outboard battery lasts as long as possible?
- Don’t leave it sitting at 80-100% all the time
- Don't leave it sitting at 0-20% all the time
- Don’t regularly run it to 0%
- Avoid storing it in hot environmentsÂ
- Partial charging is totally fineÂ
That alone will get you 90% of the way there.
1. Avoid Running It All the Way to 0%
Lithium batteries don’t like being fully drained. The system will protect itself, but you’re still putting extra stress on it every time you hit empty.
This applies whether you’re running something small like an ePropulsion Spirit 2 or a larger setup like the Momentum M10.Â
- Treat 20% as if it's zero percent. Not only does that help the longevity of your battery, but it leaves you some extra capacity as a reserve, ensuring that you can get home if you end up needing a bit more juice to do so.Â
- Running it low once in a while is fine, just don’t make it your normal routine.
- If you do get below 20%, make sure to charge your battery back to around 50% SOC as soon as possible to avoid a deeply discharged batteryÂ
2. Avoid letting your battery sit at high or low state of charge (SOC)
This is probably the most common mistake we see.
A lot of people fully charge their battery after they use it, then don’t use it again for over a week. That means it’s just sitting there at 100% for days. Or, worse, they run it down close to 0% and let it sit, risking a deep discharge.Â
- If your battery level is 20-80%, don't charge it back up to 100% right away. Wait until a day or two before you go to use it again
- If your battery level is below 20%, charge it above 20% (ideally to around 50%) as soon as possible
If you’re using removable batteries like the ePropulsion Spirit Battery Ultra, this is even easier to manage.
3. Avoid Prolonged Exposure to High and Freezing Temperatures
If there’s one thing that will quietly destroy a battery over time, it’s heat. Long exposure to freezing temperatures isn't ideal either.Â
- Avoid storing your battery in hot cars
- Don't store your battery in freezing temperatures for long periods of timeÂ
- Ideal storage temperature is typically 50°F – 77°F
4. Charging Tips (Keep It Simple)
Use the Right Charger
Stick with the manufacturer charger or a properly set up system. It's hard to mess this up for portable electric outboards because other chargers won't fit. But if you're running a larger battery like the ePropulsion E60 or E163, make sure to use the corresponding ePropulsion charger.
Partial Charging Is Totally Fine
You do not need full cycles. A partial charge is just fine!
5. Common Mistakes to Avoid
- Leaving it at 100% or close to 0% for days
- Running to 0% regularly
- Heat exposure
- Wrong charger
Final Thoughts
You don’t need to baby these batteries—you just need to avoid the obvious mistakes.
Do that, and you’ll get solid performance and a long lifespan.
Need Help With Your Setup?
If you’re trying to figure out battery sizing, runtime, or charging setup, reach out to us here—we’re happy to help.
Frequently Asked Questions
How long do electric outboard batteries last?
Most lithium batteries for electric outboards have a useful life of 7-12 years. These batteries are also rated for a certain number of charge / discharge cycles, which is typically between 800 and 3000 cycles. Refer to your user manual for specifics.Â
Should I leave my lithium battery plugged in all the time?
No. It’s fine occasionally, but not ideal long-term. Charge it right before use instead.
Is it bad to run a lithium battery to 0%?
Occasionally is fine, but don’t make it a habit. Stay above 10–20% when possible.
Can I partially charge my battery?
Yes. Lithium batteries prefer partial charging.
Do lithium batteries lose charge sitting?
Yes, about 1–3% per month.
What temperature is too hot?
Consistent temps above ~95°F will degrade the battery over time.
How long should a battery last?
Typically 5–10+ years or 800–3000 cycles at 80% depth of discharge.
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