Foil Drive Assist MAX+ and FM+ Batteries — Your Questions Answered

Foil Drive have launched their Gen 2.5 line-up, and it is a bigger change than the name suggests. There is a brand new unit — the Assist MAX+ — a completely restructured battery range that finally lets one battery work across two units, a free power upgrade for every Fusion already out there, and a handful of quieter changes to motors, pods and masts that will catch people out if nobody explains them.

We have had the full technical pack for a few weeks and have been sitting on our hands. Rather than write another launch announcement, we have put this together as the questions we already know we are going to be asked across the counter — with the actual numbers behind each answer.

If your question is not here, ring us or drop us a line. We would genuinely rather talk it through than have you guess.

+20% MAX+ thrust vs the MAX

43V Gen 2.5 architecture

648Wh FM+ 650 — fits both units

Free Fusion power upgrade

What has actually changed?

Four things, in rough order of how much they will affect you.

One. There is a new unit. The Assist MAX+ replaces the Assist MAX, and it is a Gen 2.5, 43V unit in roughly the same physical package as the old MAX. More power, more runtime, same lightweight feel.

Two. The battery range has been rebuilt around a cross-compatible family called FM+ — Fusion and MAX+. The FM+ 650 works in both units. That has never been true before.

Three. Every Fusion gets a free power increase delivered through the Foil Drive app. Not a new part, not a trade-in — a firmware update.

Four. Motor pods are no longer bundled inside the base kits, and a few accessories have moved to V2. Boring, but it changes what you actually need to order.

What is the Assist MAX+, and how is it different from the MAX?

Foil Drive describe the MAX+ as a "mini Fusion in the form factor of a MAX", and having gone through the numbers, that is a fair description rather than marketing.

Against the Gen 2 Assist MAX, the MAX+ delivers 35.5kg of maximum thrust against 29.5kg and 1750W sustained against 1455W. Both of those are a shade over 20% up. Peak boost climbs to 2150W. The unit itself measures 305 x 125 x 55mm, and a full install with the FM+ 650 battery comes in at 6.71kg.

Foil Drive position it for riders under 100kg on small to mid-length boards, and it is the unit they expect most new customers to land on. Their own guidance is that if you are 90kg or over, a Fusion is the safer pick unless you are comfortable trading some power and runtime away.

What does the 43V Gen 2.5 architecture actually change?

This is the bit worth understanding, because it explains a lot of the odd-looking numbers further down this page.

A higher voltage limits the effect of voltage drop as the battery depletes. In practice that means two things: more punch on take-off, and a greater usable depth of discharge — Foil Drive quote full power down to around 10% battery before you get noticeable sag. So the usable capacity of a 43V battery is a bigger slice of its rated capacity than it was on the 40V Gen 2 system.

That is why a smaller 43V battery can out-run a larger 40V one. It is not a typo, and it is the single most useful thing to grasp before you choose a battery.

The rest of the Gen 2.5 package: IP69 waterproofing on the batteries with the cells in a robust moulded housing, a smart BMS managing use, charging and storage, a 43V 12-amp charger in every Fusion and MAX+ box, an optional tilt sensor that cuts the motor if the board starts tipping, and auto-lock functions on the V3 controller.

The battery also stays an independent component, so if one ever gets damaged you replace the battery rather than the system.

What are the FM+ batteries, and which one do I want?

FM+ stands for Fusion and MAX+, and that is the whole point — these batteries cross between the two units. There are three Gen 2.5 batteries:

Fusion 860 — 864Wh, 20Ah, 4.9kg. Maximum runtime, and a Fusion exclusive. No adaptor needed.

FM+ 650 — 648Wh, 15Ah, 3.95kg. Available from launch, and the one Foil Drive expect to be the default. Works in the MAX+ directly, and in a Fusion with the FM+ Battery Adaptor.

FM+ 430 — 430Wh, 10Ah, 2.6kg. The sportier one, and the most interesting battery in the range for anyone chasing ride feel. Coming early 2027, so you cannot order it yet.

Why would I want a smaller battery than the one I have?

Because on a 43V system, smaller no longer means shorter.

Put the FM+ 430 in a MAX+ and compare it to the current most popular setup, the MAX High Power battery in a Gen 2 MAX. The FM+ 430 holds 430Wh against 594Wh — 28% less capacity on paper. It weighs 2.6kg against 3.15kg, so it is 17% lighter. And on Foil Drive's own indicative figures it runs five minutes longer, both in light use (50 minutes vs 45) and in heavy use (35 vs 30).

Lighter, longer, and it is sat in a unit making 20% more thrust. That is the headline of this whole launch as far as we are concerned, and it is why we think the FM+ 430 will end up being the connoisseur's pick even though it lands last.

We have put the full weight-to-power breakdown, including how all of this stacks up against the Duotone Foil Assist, in a separate post: Foil Drive vs Duotone Foil Assist — weight, power and runtime.

I have just bought a Fusion. Have I missed out?

No — and this is the answer we are most looking forward to giving, because it is the opposite of what people assume when a new unit lands.

The FM+ batteries fit a Fusion via the FM+ Battery Adaptor, which clips on tool-lessly and extends the shorter battery so it sits securely in the longer Fusion unit. Your Fusion keeps every bit of its power — 37.5kg thrust, 1850W sustained, 2370W peak boost are identical across all three batteries. What changes is what you are carrying.

A Fusion with the 860 battery is an 8.08kg install. Swap to the FM+ 650 and it is 7.13kg. Swap to the FM+ 430 and it is 5.78kg — 28% lighter than the 860 setup, with exactly the same power on tap. You trade runtime for it, obviously: 50 minutes light use instead of 90.

Which means a Fusion owner can now have a long-session battery and a sport battery and pick one on the way out the door. One unit, two completely different characters. That flexibility did not exist a month ago, and it makes the Fusion a far more interesting purchase than it was.

One thing to check: Fusions bought before 23 September 2026 need the FM+ Battery Adaptor bought separately. New Fusion base kits include it.

I own a Gen 2 Assist MAX. Can I use the new batteries?

No, and there is no workaround. The MAX is 40V and the MAX+ is 43V. They cannot share batteries or chargers, in either direction. An FM+ 650 will not run a Gen 2 MAX, and a MAX High Power battery will not run a MAX+.

That is worth knowing before you spend anything, because it means moving from MAX to MAX+ is a unit-and-battery decision rather than a unit decision.

The good news is that the Gen 2 40V batteries are continuing. The MAX High Power and MAX Sport High Power 396 stay available to service existing MAX owners, as do the Slim batteries. If you are happy with your MAX, you are not being stranded — and a three blade propeller upgrade or a high power motor is still the cheapest way to make the system you own feel newer.

Is the Assist MAX discontinued?

Yes. The Assist MAX is discontinued as of September 2026, replaced by the MAX+. Foil Drive have confirmed existing MAX customers continue to be serviced with parts and batteries. The 28V Slim Endurance battery is also being phased out during 2027, with the Slim range moving to a single battery option.

What about the Slim? Is it getting Gen 2.5?

Not yet. The Slim stays as a Gen 2, 40V unit for now — 25.5kg thrust, 1340W, and a 3.50kg install with the Performance battery, which is still comfortably the lightest way to put a motor on a foil. Foil Drive have said they intend to bring the Slim onto the 2.5 architecture in time, but the battery technology they want is not available in the quantities they need, and there is no timeline. We would not hold off buying a Slim on the strength of that.

Is the Fusion power upgrade really free?

Yes, and it is a real increase rather than a rounding error. Sustained power goes from 1750W to 1850W and peak boost from 2152W to 2368W — about 10% more thrust, delivered through the Foil Drive app.

It is the sort of thing that is easy to be cynical about until you remember the alternative is buying a new unit. Sat on the sofa, through the app, no parts.

What has changed with motors and pods?

No new motors — just a different way of selling them, and it does change what you order.

Motor pods and mast adaptors are no longer included in the MAX+ and Fusion base kits. They now come bundled with the motor instead. There are three bundles:

Retrofit High Power Motor Bundle — the Universal Mini Pod, high power stator and rotor, three blade hub and standard propellers, a 20cm removable cable and hardware. This is the go-to retrofit configuration, and it fits all foil mast brands.

Retrofit Standard Motor Bundle — the older Universal Motor Pod, standard stator and rotor, two blade hub, 30cm cable. A lower price point to get people on the water.

Integrated High Power Motor Bundle — for integrated alloy or carbon masts. An existing product with a new name.

Neither retrofit bundle is compatible with a Gen 1 Assist or Assist Plus. If you are running Gen 1, talk to us before ordering anything.

Anything else that will catch me out?

Three accessory changes worth knowing:

V2 alloy masts. The V2 integrated alloy mast now has a machined mini pod. V1 is discontinued. The cable is pre-set depending on the version: the V2 E-Foil mast is set for a Fusion, so on a MAX+, MAX or Slim you loop the cable to shorten it. The V2 Assist mast is set for MAX and Slim systems, so on a Fusion you need a Barnacle Cable Extender. V2 masts do not come with a motor.

V2 prop guard. The V1 guard is discontinued. The V2 is longer and wider and now covers all V2 motors with removable cable, V2 integrated masts, all propeller types and both pod systems. Worth having if you are learning or teaching — but it does add drag and will cost you runtime, so it is not a fit-and-forget item.

Battery caddy. Exclusive to the Fusion 860, and it works with both Gen 2 and Gen 2.5 batteries. It doubles as a USB-A and USB-C power bank, which is more useful in a car park than it sounds.

The full numbers, side by side

Every unit and battery combination Foil Drive currently publish figures for. Scroll sideways on mobile.

Runtime figures are Foil Drive's indicative averages for an 85kg intermediate rider on an 800–1000cm² wing and a 5'0 40L board in under 5 knots of wind. Your session will vary with skill, weight, gear sizing and conditions. Install weight includes unit, battery, integrated high power motor, three blade hub and propellers, and nose cone where applicable — a retrofit install with the mini pod mounted at 20cm adds 360g.