Can Your Motorcycle Power Heated Gear? How to Work Out the Numbers
Gear
Published
Heated jackets, gloves and grips all draw on the same charging system. Here is how to find a motorcycle's spare capacity, add up the load, and test whether it copes.
Most motorcycles will run a heated jacket or a set of heated grips. Far fewer will run a jacket, gloves and grips at the same time. The deciding number is not battery size — it is how much power the charging system makes beyond what the motorcycle already consumes to run itself. A full set of heated clothing can ask for twelve amps or more, on the order of 150 watts, and on a smaller or older machine that exceeds the surplus available. Working out whether a particular bike copes takes a spec figure, some arithmetic, and a voltmeter.
What heated gear actually draws
Manufacturers publish current draw in amps rather than watts, because amps are what matters for fuse sizing. Converting is simple: watts equal volts multiplied by amps. A motorcycle's electrical system sits at a nominal 12 volts but runs nearer 13 to 14.5 volts once the engine is turning, so the same garment represents a slightly different wattage depending on which figure is used.
These are published or independently measured figures for commonly used items:
| Item | Current draw | Approximate power at 12–14 volts |
|---|---|---|
| Heated jacket liner (Gerbing) | 6.4 amps | 77–90 watts |
| Heated jacket (Keis J601 Ultraflex, full power) | around 5.4 amps | 65–76 watts |
| Heated gloves (Gerbing) | 2.2 amps | 26–31 watts |
| Heated grips (Oxford HotGrips, measured at full power) | 3.29 amps measured, 4 amps claimed maximum | 40–56 watts |
| Heated seat cushion (Keis) | 1.4 amps | 15 watts (stated) |
Gerbing states that its jacket liner and gloves together draw 8.6 amps. Add heated grips to that and the total approaches twelve amps, which is where riders start to run into trouble on bikes that were never designed with much headroom.
Two caveats before the sums begin. These are maximum figures — gear run through a thermostatic controller at half power draws roughly half as much, and few riders sit on full heat all day. And figures vary between models within a brand, so the number that matters is the one printed on the garment or its manual.
Where the spare capacity comes from
The battery is not the power source while riding. It is a buffer. The alternator or stator makes the electricity, the regulator-rectifier conditions it, and whatever is left after the motorcycle's own needs are met is what remains for accessories. Run a bigger load than the charging system makes and the shortfall comes out of the battery, which then flattens over the course of a ride regardless of how new or large it is.
The headline output figure flatters reality in one important way. As Rider magazine's guidance on adding electrical accessories puts it, a quoted output is "400 watts at a given rpm (revolutions per minute), often corresponding to highway speeds in top gear. At lower rpm, such as trolling through town in traffic, the output will be lower."
That caveat matters more in cold weather than at any other time, because the conditions that make heated gear necessary — an alpine pass in late autumn, a dark, slow descent, a queue at a border crossing — are exactly the conditions where engine speed is lowest and demand is highest. A system that balances comfortably at motorway cruising speed can run a deficit in traffic.
The three-step sum
The arithmetic is not complicated, and it is worth doing before buying anything.
- Find the total output. This appears in the workshop or service manual, and sometimes in a manufacturer's full specification. It is given in watts, or in amps at a stated engine speed. Owner's handbooks frequently omit it; the service manual rarely does.
- Subtract what the motorcycle uses. Rider's method is to work through the always-on loads — headlights, tail light, instrument lights and running lights — and subtract each from the total. Fuel injection and the fuel pump also draw current; the manual will give those figures, and the draw is usually modest. Indicators and the brake light are intermittent, but on a dark, wet evening they are effectively continuous.
- Compare the remainder against the heated gear total. What is left is the working surplus. If a full heated outfit consumes most of it, the margin has gone.
Some manufacturers shortcut all of this by publishing a maximum accessory load in the handbook. Where that figure exists, it is the authoritative one and it supersedes any calculation — it already accounts for the bike's own consumption.
There is no published universal rule for how much margin to leave, so any specific percentage circulating on forums is opinion rather than specification. The practical approach is to size the load conservatively and verify it by measurement — the only method that accounts for a particular motorcycle rather than an idealised one.
The test that settles it
A voltmeter across the battery terminals is the arbiter, and it costs very little. Yuasa's technical manual sets out both the method and the figures: connect a digital voltmeter directly to the battery terminals, start the engine, and hold it between 3,000 and 4,000 rpm while watching the reading. If the system "maintains voltage between 13.0 and 14.5 volts, the charging system is probably working properly". If the voltage is "the same as open circuit voltage (usually less than 13 volts) the charging system is not working".
Applied to heated gear, the test becomes a load test. Run it twice: once with everything switched off, and again with every heated item on full, headlight on, and the engine at a realistic road speed. If the voltage stays inside the Yuasa band in both cases, the system is coping. If it sags toward resting battery voltage only when the gear is switched on, the charging system is being asked for more than it makes, and the battery is covering the difference.
Repeating the measurement at idle is revealing, and usually sobering. Many systems that are comfortable at 4,000 rpm fall into deficit at a standstill. That is not necessarily a problem on a flowing ride, but it matters on a cold morning spent queueing.
A permanently mounted voltmeter turns this one-off check into continuous information. Rider recommends fitting one specifically to "let you know right away if you're asking for more power than it can safely give you". Several heated-grip controllers include a protective cut-off instead — the Oxford units, for instance, disengage if battery voltage drops below 11.5 volts.
Wiring it so it survives the trip
How heated gear is connected matters as much as whether the capacity exists.
Fuse the circuit properly. Keis advises adding up the amp rating of all garments and choosing the next fuse size up. Gerbing applies the same logic to its own 8.6-amp jacket-and-gloves combination and specifies a 10-amp fuse. A fuse sized far above the load protects nothing; one sized below it will strand a rider at the worst moment.
Be careful with accessory sockets. This is where modern machines trip people up. Gerbing warns that bikes using a CAN bus (Controller Area Network) accessory socket may limit how much current that socket will pass, and advises checking with the motorcycle manufacturer what the system will tolerate. The company describes a lead taken directly from the battery as the most fail-safe approach on newer bikes. An accessory socket rated for a phone charger will not necessarily carry a heated jacket.
Switch it through a relay. The recommended arrangement is a distribution block connected to the battery terminals but triggered through the ignition circuit by a relay, so accessories are only live with the ignition on. This prevents the slow flattening that comes from a forgotten controller, and keeps high-current loads off the bike's own switchgear.
If the numbers do not add up
A charging system that cannot run a full outfit is not the end of the matter.
- Heat the core, not everything. A vest draws considerably less than a full jacket and delivers most of the benefit, because warming the torso is what keeps blood flowing to the extremities.
- Use the controller. A thermostatic controller held at a third or half power cuts the draw proportionally. Most riders find continuous full heat uncomfortable anyway.
- Stagger the load. Grips and gloves do similar work. Running both at full output is usually redundant.
- Consider battery-powered garments. These bypass the charging system entirely, at the cost of limited run time, and suit riders whose bikes have little or no surplus.
- Improve the passive insulation first. Windproofing, a proper neck seal and eliminating draughts at the wrists and collar reduce how much heat has to be added electrically in the first place.
Before a cold-weather trip
A short checklist, worth running before leaving rather than at a petrol station in the dark:
- Confirm the charging system output from the service manual, or the maximum accessory load from the handbook if one is published
- Add up the draw of every heated item actually being taken
- Check the fuse rating against that total
- Run the voltmeter test with everything switched on, at road speed and at idle
- Carry spare fuses of the correct rating, and know where the fuse box is
- Confirm whether the accessory socket is current-limited before relying on it
Route choice feeds into this more than it first appears. Altitude, time of day and how much of the ride is slow or urban change both how cold it gets and how much the charging system produces. Sketching the day out in advance makes it clear whether the demanding stretch coincides with the low-output stretch — the Travel Riders route planner is a straightforward way to see where the climbs and the long slow sections land.
Treat every figure quoted here as a starting point, not a specification for a particular motorcycle. Models differ, charging systems age, and a stator that met its rated output when new may not now. The voltmeter is the one check that reflects the machine in the garage rather than the one in the brochure — worth doing before the first genuinely cold ride of the season, not during it.
Planning a cold-weather route this season? Lay it out in the Travel Riders route planner, export it to a satellite navigation device, and head off knowing where the cold sections fall — and that the bike can keep you warm through them.