Foil Drive Battery Guide: Which Foil Drive Battery Should You Choose?
October 2026 update: this is the legacy Gen 2 battery reference
The Foil Drive MAX+ Gen 2.5 has now replaced the original Assist MAX as the current all-round Foil Drive system, alongside Foil Drive Fusion. The new 43V FM+ battery family is not interchangeable with original Gen 2 MAX or Slim batteries and chargers.
This older guide remains useful for riders who own, maintain or are considering a discounted Gen 2 kit. For an up-to-date comparison of all current and older battery families, start with our Foil Drive Battery Guide: MAX+, Fusion, MAX & Slim.
| Your system | Battery route |
|---|---|
| Assist MAX / Slim Gen 2 | Use only batteries and chargers approved for that exact Gen 2 system |
| Assist MAX+ Gen 2.5 | FM+ 650 and the correct 43V charger |
| Fusion Gen 2.5 | Fusion 860 or FM+ 650 with the correct adaptor |
Battery capacity figures in the sections below are reference information for the named products, not a recommendation that legacy batteries will fit the latest kit.
Choosing a Foil Drive battery used to be fairly straightforward. It is not any more.
The Foil Drive range has expanded from lightweight assist batteries into a proper family of power options covering the Assist Slim, Assist MAX the previous-generation battery family and the newer Foil Drive Fusion.
That is good news because you can tune a Foil Drive setup much more closely to the way you actually ride. The downside is that simply buying the biggest battery is not necessarily the right answer.
A surf foiler trying to keep a small board lively has very different requirements from a heavier rider learning flat-water starts. A downwind rider may value repeated starts and low weight, while somebody using Foil Drive almost like an eFoil will naturally prioritise capacity.
This guide explains the main Foil Drive batteries available from The SUP Company, what the numbers actually mean and which battery makes sense for different riders.
The quick answer: which Foil Drive battery should I buy?
| Battery | Capacity | System | Best for |
|---|---|---|---|
| Foil Drive Slim Performance Battery | 166.32Wh | Assist Slim | Lightweight, performance-focused assist |
| Foil Drive Slim Travel Battery | Travel-focused | Assist Slim | Travelling riders wanting the Slim platform |
| Foil Drive MAX Sport Battery | 332.64Wh | Assist MAX | Lightweight MAX setups and shorter assist sessions |
| Foil Drive MAX Travel Battery | 356.6Wh | Assist MAX | MAX riders who regularly travel |
| Foil Drive MAX Sport High Power 396 Battery | 396Wh | Assist MAX | Our pick for performance-focused MAX riders |
| Foil Drive MAX Power Battery | 498.69Wh | Assist MAX | Legacy higher-capacity MAX option |
| Foil Drive MAX High Power Battery | 594Wh | Assist MAX | Maximum MAX runtime and High Power performance |
| Foil Drive Fusion 860 Battery | 864Wh | Fusion | Long sessions, learning and hybrid eFoil/assist use |
The simplest way to think about it: choose Slim when minimum weight matters most, MAX when you want the broadest balance of performance and runtime, and Fusion when significant motor use and outright range become priorities.
Why does Foil Drive battery size matter so much?
Watt-hours, normally written as Wh, tell you roughly how much energy a battery can store.
A 594Wh battery contains considerably more usable energy than a 166Wh battery, but that does not automatically make it better.
Extra battery capacity normally means extra weight and physical size. On a conventional eFoil that may not matter enormously. On a surf foil or downwind board, it absolutely does.
Weight attached underneath the board affects how easily the board:
- pumps;
- accelerates onto foil;
- changes direction;
- unweights through turns;
- responds when connecting bumps or waves.
This is why Foil Drive now offers such a broad battery range. The objective is not simply to maximise runtime. It is to find the amount of battery that suits the job.
Foil Drive Assist Slim batteries
The Foil Drive Assist Slim Gen 2 is the lighter, more discreet side of the Foil Drive family.
It makes most sense when the motor is there primarily to help you start rather than power you around for long periods.
Foil Drive Slim Performance Battery – the lightest performance choice
The Foil Drive Slim Performance Battery is a 166.32Wh, 40V battery weighing approximately 1kg.
This is the battery to choose if maintaining natural foil feel matters more than having a huge amount of stored energy.
It particularly suits competent riders using Foil Drive for:
- surf foiling;
- prone foiling;
- wing foiling;
- SUP foiling;
- downwind starts;
- occasional recovery assistance.
Think of it as a start-assist battery rather than a motor-around-all-day battery.
If you can already foil efficiently and mainly want the motor to increase your number of successful starts, this can be a much nicer setup than carrying battery capacity you rarely use.
Foil Drive Slim Travel Battery – for the rider who flies with their kit
The Foil Drive Slim Travel Battery applies the same lightweight philosophy to riders who travel.
Its big attraction is the split battery construction. Instead of carrying one conventional large lithium battery, the travel system separates into smaller sections for transport.
That can make travelling with Foil Drive considerably more realistic.
There is an important caveat: never assume a battery is automatically approved for your flight simply because it is described as a travel battery. Airline lithium battery rules vary, approval can be required in advance and rules can change.
Always contact the airline before travelling.
Foil Drive Assist MAX batteries
For most riders looking for serious Foil Drive assistance, the Foil Drive Assist MAX Gen 2 is where the battery discussion becomes particularly interesting.
MAX gives you much greater choice. You can build it light, build it for range, build it for travel or combine it with the High Power motor and battery for substantially more assistance.
Foil Drive MAX Sport Battery – lightweight MAX
The original Foil Drive MAX Sport Battery has a capacity of 332.64Wh.
Its purpose is simple: give you the benefits and electronics of the Assist MAX platform without hanging one of the larger MAX batteries underneath the board.
Choose the original MAX Sport if you:
- want to keep your MAX relatively light;
- use the motor mainly for starts;
- surf foil or downwind where board response matters;
- already foil efficiently;
- do not regularly exhaust a larger battery.
The downside is straightforward: less stored energy means less runtime.
Foil Drive MAX Sport High Power 396 Battery – possibly the sweet spot
This is one of the most interesting recent additions to the Foil Drive battery family.
The Foil Drive MAX Sport High Power 396 Battery increases capacity to 396Wh while remaining much smaller and lighter than the MAX High Power battery.
It weighs approximately 1.85kg and gives around 20% more capacity than the original 332.64Wh MAX Sport.
That makes it particularly attractive because it addresses one of the biggest compromises in a Foil Drive setup: how do you add useful runtime without making a performance foil board feel unnecessarily heavy?
Choose the MAX Sport High Power 396 if you want a responsive MAX rather than the longest-running MAX.
It makes a lot of sense for:
- surf foiling;
- downwind foiling;
- parawinging;
- wing foiling;
- smaller boards;
- riders who pump and link waves;
- experienced riders who use the motor strategically.
Foil Drive quotes approximate assist sessions of around 25–40 minutes with heavy motor use and 30–55 minutes with lighter motor use, although real-world runtime varies enormously with rider weight, foil, board, water state, temperature and throttle use.
For many experienced foil-assist riders, we think this is a particularly clever battery because it prioritises usable capacity per kilogram rather than simply chasing the biggest number.
You can currently browse it alongside the rest of our Foil Drive battery range.
Foil Drive MAX Travel Battery – more capacity with travel flexibility
The Foil Drive MAX Travel Battery has a capacity of approximately 356.6Wh and is designed specifically around travelling with an Assist MAX.
It uses a modular split construction while reassembling into a proper MAX battery at your destination.
This is a specialist choice rather than automatically the battery we would recommend for somebody who never flies.
Choose it if travel genuinely matters. If virtually all your riding is from home, a conventional battery will normally be the more straightforward route.
Foil Drive MAX Power Battery – the older 498.69Wh option
The Foil Drive MAX Battery listing also references the 498.69Wh MAX Power battery.
This was the traditional higher-capacity step above MAX Sport and remains relevant for riders who already own one or encounter remaining stock.
However, Foil Drive now classifies the MAX Power as a discontinued model, with the newer High Power range taking over at the performance end of the line-up.
That does not suddenly make a MAX Power battery bad. A 498.69Wh MAX Power remains a very useful amount of capacity and an excellent battery to own.
It simply means that if you are building a brand-new top-spec system today, we would normally start the conversation with the newer 396Wh Sport High Power or 594Wh MAX High Power batteries depending on your priorities.
Foil Drive MAX High Power Battery – maximum Assist MAX performance
The Foil Drive MAX High Power Battery is the serious option.
Capacity rises to 594Wh, making it the largest battery in the Assist MAX family.
This is not simply a battery for somebody who wants to see the biggest number on the specification sheet.
It makes sense when you actually need what it offers.
That includes:
- heavier riders;
- smaller or lower-volume boards;
- smaller and faster foils;
- frequent flat-water starts;
- long downwind sessions;
- strong current or headwinds;
- riders who use the motor heavily;
- customers wanting the full High Power MAX setup.
When paired with the Foil Drive MAX High Power Motor, this is also the battery that unlocks the full High Power performance envelope, including Foil Drive's maximum boost mode.
The battery itself weighs approximately 2.8kg.
That extra mass is why we would not automatically put it underneath every performance foil board.
If you spend an hour surf foiling but only touch the motor briefly to catch each wave, carrying 594Wh may be unnecessary. If you are 95kg, trying to get a compact board flying in difficult conditions and relying heavily on assistance, it can transform the experience.
Battery choice needs to match motor usage, not ego.
Foil Drive Fusion 860 Battery – a different category altogether
Then there is Fusion.
The Foil Drive Fusion Complete Kit uses the dedicated Fusion 860 battery with 864Wh of capacity.
This is a substantial jump from Assist MAX.
Fusion operates on its own 43V architecture and has been created to sit between conventional foil assist and a full eFoil.
You can position the motor higher on the mast and use it primarily to assist take-off, or position it lower for much more sustained powered riding.
This makes the Fusion 860 particularly well suited to:
- flat-water foil progression;
- heavier riders;
- long-distance powered exploration;
- repeated learning attempts;
- surf access;
- downwind training;
- riders wanting one system to bridge foil assist and eFoil-style use.
The 864Wh Fusion battery is a one-piece battery with its own battery-management architecture and is fundamentally different from the batteries used with Assist MAX or Assist Slim.
Fusion, MAX and Slim batteries are not interchangeable simply because they all carry the Foil Drive name.
Foil Drive battery capacity comparison
| Battery | Capacity | Approx. positioning |
|---|---|---|
| Slim Performance | 166.32Wh | Minimum weight |
| MAX Sport | 332.64Wh | Light MAX |
| MAX Travel | 356.6Wh | Travel-focused MAX |
| MAX Sport High Power 396 | 396Wh | Performance sweet spot |
| MAX Power | 498.69Wh | Legacy high-capacity MAX |
| MAX High Power | 594Wh | Maximum Assist MAX |
| Fusion 860 | 864Wh | Extended powered/hybrid use |
Which Foil Drive battery is best for surf foiling?
For a skilled surf foiler, we would normally lean towards lower weight rather than maximum capacity.
The Slim Performance makes sense if you want the lightest overall Assist Slim platform.
For Assist MAX riders, the new MAX Sport High Power 396 is particularly appealing. Its combination of 396Wh capacity and relatively low 1.85kg weight keeps a board noticeably more responsive than fitting the largest battery simply for the sake of it.
If your session involves motoring significant distances between peaks or using heavy throttle repeatedly, the MAX High Power becomes more relevant.
Which Foil Drive battery is best for downwinding?
This depends heavily on your ability.
A strong downwind rider may use Foil Drive only for the initial start and the occasional reset. For them, reducing weight can improve pumping and connection between bumps.
A progressing downwind rider may make many more powered attempts during a session. That pushes the decision towards a larger MAX battery.
For dedicated training sessions where maximum attempts matter, the MAX High Power gives you substantially more reserve.
For very long powered sessions or riders wanting much more than start assistance, Fusion starts to make sense.
Which battery is best for heavier riders?
Heavier riders tend to require more energy to accelerate the board to take-off speed, particularly when using smaller boards or faster foils.
For that reason, we generally favour the Assist MAX platform over Slim when significant assistance is required.
The MAX High Power 594Wh paired with the High Power motor is the obvious Assist MAX option when maximum support matters.
If you are looking for sustained power as well as foil assistance, the Fusion 860 takes another significant step up.
Which Foil Drive battery is best for wing foiling?
Wing foilers often need much less motor time than people expect.
You may only need assistance through a lull, to release a small board or to get the foil moving before the wing takes over.
For an experienced wing foiler, that makes the lighter batteries extremely attractive.
A Slim Performance setup can be wonderfully discreet, while the MAX Sport High Power 396 gives a useful middle ground for riders who want more reserve without turning their MAX into the heaviest possible configuration.
Should I buy one large Foil Drive battery or two smaller batteries?
This is an excellent question.
For some riders, two smaller batteries are more useful than permanently carrying the largest possible battery.
You can ride a lighter setup, return to the van or beach when required and swap batteries for another session.
This approach makes particular sense when:
- your riding spot is close to your vehicle;
- you normally ride several shorter sessions;
- board response is important;
- you share the Foil Drive;
- you want redundancy rather than one very large battery.
A single large battery makes more sense when changing batteries during a session is impractical or when you are travelling significant distances from your launch point.
Remember: quoted runtime is only a guide
Foil Drive battery runtime can never sensibly be reduced to one universal number.
A 75kg experienced foiler using five-second bursts has completely different energy consumption from a 100kg rider holding substantial throttle while learning flat-water starts.
Runtime changes with:
- rider weight;
- foil size and efficiency;
- board size and drag;
- propeller choice;
- motor height;
- wind and current;
- water temperature;
- throttle level;
- how often the motor is used;
- battery condition and age.
We would always rather choose a battery around your actual riding than promise a runtime figure that may bear little resemblance to your session.
Can I use any Foil Drive battery with any Foil Drive system?
No.
This is one of the most important points in this guide.
- Assist Slim batteries are designed for the Slim system.
- Assist MAX batteries are designed for the MAX system.
- Fusion batteries use the dedicated Fusion architecture.
Do not assume that voltage, plugs, charging equipment or battery management are interchangeable.
If you already own a Foil Drive and are unsure which generation or electronics box you have, contact us before ordering a replacement battery.
Try Foil Drive before you decide
Battery specifications tell you plenty, but they do not tell you how several kilograms of additional battery feels underneath your own style of board.
That is why foil assist is one of the categories where proper advice and testing can be particularly useful.
Selected Foil Drive systems can be explored through our Try It Now service at The SUP Co x Lymington, subject to suitability, equipment availability and rider experience.
We can also help you work backwards from your riding rather than simply selling you the biggest battery:
- your weight;
- your board;
- foil brand and front wing;
- mast;
- discipline;
- how competent you already are;
- how much you expect to use the motor.
That information usually makes the correct battery choice much clearer.
Our Foil Drive battery recommendations
Best for minimum weight: Foil Drive Slim Performance Battery.
Best MAX battery for performance-focused riding: Foil Drive MAX Sport High Power 396 Battery.
Best for maximum Assist MAX runtime and power: Foil Drive MAX High Power Battery.
Best for flying with Foil Drive: choose the appropriate Slim Travel or MAX Travel Battery, subject to airline approval.
Best for long-duration powered use: the 864Wh battery supplied with the Foil Drive Fusion.
If you are still deciding between the complete systems rather than simply choosing a battery, our foil assist guide and Duotone Foil Assist vs Foil Drive comparison are useful next reads.
Foil Drive battery FAQs
What is the best Foil Drive battery?
There is no single best battery. For performance-focused Assist MAX riders, the MAX Sport High Power 396 is an excellent balance of capacity and weight. Choose MAX High Power 594Wh if runtime and maximum assistance matter more. For the lightest setup, look at Assist Slim.
What is the biggest Foil Drive battery?
The Foil Drive Fusion 860 has 864Wh of capacity. Within the Assist MAX range, the MAX High Power battery is the largest current option at 594Wh.
Is the MAX Sport High Power 396 better than the MAX High Power 594?
Not universally. The 396Wh battery is lighter and better suited to riders prioritising board response, pumping and manoeuvrability. The 594Wh battery offers substantially greater capacity and is better for heavy motor use, heavier riders and longer sessions.
Can I use a MAX battery in an Assist Slim?
No. Assist MAX and Assist Slim use different battery formats. Order the battery specifically designed for your system.
Can I use an Assist MAX battery with Foil Drive Fusion?
No. Fusion uses a dedicated 43V power architecture and Fusion-specific battery and charging equipment.
Is the Foil Drive MAX Power battery discontinued?
Foil Drive now lists the 498.69Wh MAX Power as discontinued. It remains a perfectly useful battery for existing owners, but the newer MAX Sport High Power 396 and MAX High Power 594Wh batteries now provide the more current buying routes.
Can I take a Foil Drive battery on an aeroplane?
Foil Drive produces dedicated travel battery options, but airline rules vary and lithium battery transport normally requires careful checking. Always obtain confirmation from your airline before travelling rather than assuming a battery will be accepted.
How long does a Foil Drive battery last?
There is no universal runtime because motor usage varies enormously. Rider weight, foil, board, propeller, conditions and throttle use all affect consumption. A rider using short take-off bursts can have a much longer overall session than somebody riding continuously under power.
Should I buy a spare Foil Drive battery?
A spare can be very useful if you regularly ride back-to-back sessions or prefer using a lighter battery rather than carrying maximum capacity all the time. Tell us how and where you ride and we can help work out whether one larger battery or two smaller batteries makes more sense.
Can I try Foil Drive before buying?
Selected foil assist equipment may be available through our Lymington Try It Now service. Demos are subject to suitability, availability and approval, but they can be particularly useful when deciding whether the additional power and weight of a larger battery is worthwhile for your riding.
Need help choosing your Foil Drive battery?
Foil Drive is modular enough that getting the battery right makes a genuine difference to the finished setup.
If you are unsure, send The SUP Company your rider weight, board, foil, current Foil Drive system and the type of riding you do. We can help determine whether you actually need maximum capacity or whether a lighter battery will make your setup more enjoyable.
Browse our Foil Drive batteries, explore the wider Foil Drive range, or visit The SUP Co x Lymington for specialist wing, foil and electric-assist advice.
Finance options are available on qualifying orders, which can be useful when investing in a complete Foil Drive setup. Battery availability can change, so if you need a particular battery for a trip, upgrade or new build, contact the team to confirm current stock and compatibility before ordering.