Electric Mountain Bike Range: What 500, 625, or 750 Wh Really Gets You

What 500, 625, or 750 Wh actually measures

135 miles (218 km). That’s the range Bosch’s online calculator shows when you open its UK version, with a Performance Line PX motor and an 800 Wh battery [1]. It’s a promise the calculator can keep, as long as you read the default settings: ECO mode, an 11 mph (18 km/h) average, 220 lb (100 kg) including bike and gear, some inclines, a light breeze, mostly smooth pavement, and summer [1]. Not exactly a mountain bike ride.

Let’s start with the unit. The watt-hour (Wh) measures an amount of energy: what a 1 W device uses in one hour. A battery’s capacity is its voltage multiplied by its charge in amp-hours: Gazelle, for example, lists 13.8 Ah for its 500 Wh Bosch battery [2], which works out to about 36 V. For a sense of scale, a 4,000 mAh phone battery at 3.85 V stores about 15 Wh, so a 625 Wh battery holds as much as roughly forty of them.

So the number tells you how much energy the battery carries, not how many miles it will last. As with a headlamp’s runtime, a claimed distance only holds under its own assumptions. And on a mountain bike, it’s mostly elevation gain that sets the price of every mile.

What a climb costs in watt-hours

Let’s do the math. Lifting a mass takes energy equal to the mass times gravity times the height, and the physics is simplest in metric units. For 100 kg (220 lb), rider, bike, and backpack included, and 1,000 m (3,281 ft) of elevation gain: 100 × 9.81 × 1,000, or 981,000 joules, which is 272 Wh. That’s a minimum: it leaves out rolling resistance, air drag, and the motor’s losses.

You share that energy with the motor, and the assist percentage tells you in what proportion. At 300%, the motor puts in three times your effort, so three-quarters of the total: about 200 Wh per 3,281 ft (1,000 m). E-MTB motors go further: on its UK website, Bosch says its Performance Line CX delivers up to 600% assist below 9.3 mph (15 km/h), once updated [3]. The motor then supplies six-sevenths of the effort, about 234 Wh per 3,281 ft (1,000 m).

On paper, then, a 625 Wh battery would climb about 9,800 ft (3,000 m) at 300% assist. In practice, a lot less: rolling resistance on dirt, air drag, and motor losses all add up, and the descent doesn’t recharge the battery. Compare that with Bosch’s calculator: its 135 miles (218 km) on 800 Wh assume less than 6 Wh per mile (under 4 Wh per km), while a 3,281 ft (1,000 m) climb spread over 6.2 miles (10 km) already takes about 33 Wh per mile (about 20 Wh per km) at 300%.

Enlarge diagram

Weight, mode, cadence, cold: what drains the battery

On climbs, weight counts in direct proportion: an extra 22 lb (10 kg) on top of 220 lb (100 kg) means 10% more energy for the same elevation gain. That’s why Bosch advises against carrying any unnecessary weight, bike and gear included [4].

The assist mode matters even more. For the same bike with a 500 Wh Bosch battery, Gazelle’s French website lists up to 112 miles (180 km) in Eco mode and 43 miles (70 km) in Turbo [2]: two and a half times less range from the same battery.

Those numbers translate into energy per mile: 112 miles (180 km) on 500 Wh is under 4.5 Wh per mile (under 3 Wh per km) in Eco mode; 43 miles (70 km) is about 11.5 Wh per mile (just over 7 Wh per km) in Turbo. These are maximums, reached in good conditions, and Gazelle lists the factors that bring them down [2].

How you pedal matters too. Above 50 pedal revolutions per minute, the motor runs more efficiently, while a very slow cadence burns a lot of energy; frequent starts and stops cost more than a steady speed [4]. Bosch also recommends riding at the maximum permitted tire pressure to cut rolling resistance [4]. That advice is for the road: on a mountain bike, you pick your pressure for traction first, and your range pays the price.

Then there’s the cold. As the temperature drops, the battery’s electrical resistance rises and its performance falls: Bosch warns that you should expect less range in winter [4]. Age works the same way: Bosch’s calculator notes that its figures apply to a new battery, whose performance declines over time, as with any lithium-ion battery [1].

Range over time: aging and storage

A lithium-ion battery loses capacity over the years, whether you ride it or not, and your range drops with it. Bosch lists what speeds up that wear: heavy use, storage above 86 °F (30 °C), long-term storage fully charged or fully drained, and parking the bike in direct sun [4].

On the flip side, moderate use and storage at 59 to 68 °F (15 to 20 °C), at about 60% charge, go easy on it [4]. The same guide says it doesn’t discharge on its own over a winter break: no need to recharge it before your next ride if you stored it at 60% [4]. In other words, for the winter: not full, not empty, not in a freezing garage, and not on a sunny windowsill.

Manufacturers’ range calculators, and what they assume

Manufacturers publish ranges, always based on assumptions. Bosch’s battery guide from 2015 laid out three scenarios: ideal conditions, with flat terrain, about 9.3 mph (15 km/h), no headwind, and a rider under 154 lb (70 kg); mixed conditions, with moderate hills, about 12 mph (20 km/h), and 154 to 176 lb (70 to 80 kg); and tough conditions, with mountainous terrain, about 15.5 mph (25 km/h), a headwind, and over 187 lb (85 kg) [4]. An e-MTB in the mountains lives in that third column full-time.

Bosch’s online calculator goes further: you can set the mode, average speed, total weight, cadence, terrain, wind, surface, tires, and season [1]. It’s a good tool, as long as you set it for your ride instead of trusting its defaults. At a minimum, set the terrain, your real weight with gear, and the season you’ll ride in: those are the three settings the defaults flatter most. Gazelle lists the same factors: shifting, tire pressure, weight, speed, terrain, headwind, battery age, and assist level [2].

For a mountain bike ride, I trust the math over the spec sheet: add up the elevation gain, multiply it by the energy the climb takes in the mode you plan to use, then keep a margin of at least a third for rolling resistance, air drag, losses, and the cold. It’s the same reasoning as sizing a camper van’s house battery: an energy budget, not a promise of miles.

On an electric mountain bike, range is measured in feet of climbing, not in miles.

Worth watching

EMBN walks through what decides an e-MTB’s range, from battery size, rider weight, and power mode to trail conditions, tires, elevation, and riding style, plus how a range finder helps.

The video is hosted by YouTube (Google): nothing loads until you play it, and Google may then set cookies.

Julien de Jurquet

Vans, RVs, biking and calculators

Julien de Jurquet writes for Outfarer about camper vans, RVs, biking, and calculators. He reads manuals cover to cover and never lets a number slide without its unit, so your choices rest on math, not promises.

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