8 things that drain an e-bike's battery and how to avoid them

As with electric cars, range anxiety can be at the back of the mind of e-bike riders. No-one wants to be hauling the extra weight of a flat battery up the last hill before reaching home. There’s plenty you can do to extend your e-bike’s battery range though, however limited it may look on paper.

Clearly, the e-bike battery’s capacity will be a key determinant of your range. There’s a compromise that designers need to make between having abundant range and the additional weight that a larger battery will have. Where they draw that line will depend on the electric bike’s intended use. 

At one extreme, electric mountain bikes and some electric hybrid bikes have high capacity batteries, in the former to power their high torque motors up steep ascents and in the latter to provide range and assistance for urban riding.

At the other extreme, lightweight electric road bikes and folding e-bikes tend to have lower battery capacity, in the case of road bikes to offer a sporty ride feel and for folding e-bikes to make them easier to move around. 

Many of the best electric bikes allow you to buy a separate, external range extender battery. This usually sits in a bottle cage or where one would normally be placed and plugs into the battery in the frame. Typically, a range extender will add around 50 percent to an electric bike’s range.

Beyond choosing an e-bike with a suitable battery capacity for its expected use, there’s plenty that you can do to extend your e-bike’s range. Here are some key factors that affect range and what you can do to help increase it.

Riding in 'turbo mode'

The more pedal power you put in, the less a motor will have to work, and so the longer the range you’ll have. If you're relying on the motor to keep you moving, you’ll get close to the stated range, but you can extend that greatly by putting in more of the propulsion yourself.

Most electric bikes allow you to select the level of assistance you want, with usually between three and five options. You can also ride an electric bike without assistance. In many cases, there’s little or no added resistance from the motor when it’s turned off, although you’ll have the extra weight of the motor and battery to move.

To extend your range, it’s a good idea to vary your assistance level, so that you save higher levers for when they’re needed and reduce the assistance when you can get along with less.  

Hilly routes 

If you ride in a hilly area, your e-bike’s motor is likely to be working harder than on the flat to help to pull you up the inclines. You will probably want to select a higher assistance level too. Both will reduce the available range.

Unlike electric cars, electric bikes don’t normally have regenerative braking, so you’ll not recharge the battery on downhills, with energy dissipated instead as heat from use of the e-bike’s brakes.

Stop/start riding is also likely to reduce range, as the motor will be providing more input to help you to accelerate, so riding around town is likely to be more battery-intensive than cruising in the countryside.

Spending more time below the assistance cut off

In much of the world, electric bikes have to cease motor input once your speed exceeds 25kph/15.5mph. For a fit rider on a lighter electric bike, that’s likely to be easily achievable on the flat. Since the motor won’t be working above this speed, you’ll not be using up the e-bike’s battery capacity.

The exception is the US, where assistance cuts out at 20mph or 28mph, depending on the e-bike class. In both cases, it’s likely that the motor will be working much of the time, so there’ll be more drain on the battery. 

Headwinds 

As when riding an unassisted bike, a stiff headwind is a lot harder to ride into than riding with a tailwind or on a still day. That’s going to mean greater drain on your battery, as you’ll need greater support from your motor. 

So it will help extend your available range if you can avoid riding into the wind. If you can plan your ride so that you have the headwind on the way out, when you’re fresher, and have a tailwind on the way home, you may increase your battery’s range a little. 

Storing the battery in cold temperatures 

The temperature at which your battery has to operate will affect its range, with available capacity reducing at lower temperatures. If you’re riding when it’s below 50F/10C outdoors, storing your battery indoors may help you to increase your available range. 

There’s some internal heat generated as the battery discharges, which will help to increase its efficiency once you’re riding.

Not making the most of available software 

Many electric bikes will have a display on the bike or a phone app that will tell you the range available. Some are more clever. 

Specialized’s e-bike app, for example, allows you to input your riding distance and route. It will then calculate an assistance level that will provide you the support that you need but still ensure that the battery will not run flat before you get home.

You can also fine-tune Specialized’s motor’s support levels to match your requirements, again offering an opportunity to extend range.

The Mahle ebikemotion rear hub motor, a popular system used on many lightweight electric bikes, can be linked up to a Bluetooth heart rate monitor. You can use its SmartBike app to set the assistance to cut in when your heart rate exceeds a specified level. 

You can choose between three pre-configured power output profiles or, as with the Specialized app, customize the three available assistance levels to suit your own requirements.

Leaving the battery on the bike, unused 

An electric bike battery will slowly discharge, even when the e-bike is not in use. If you’re not planning to ride over winter, for example, you will probably need to recharge the battery before taking your e-bike out again in the spring.

If your e-bike has a removable battery, it’s generally recommended that you store it off the bike when you’re not riding for an extended period, as there’s background drain from the e-bike’s electronics even when it's not in use.

Fully discharging the battery, and age 

All lithium ion batteries slowly lose capacity over time. How fast this occurs depends on a number of factors, including the number of charging cycles and how low you run them, with repeated full discharge reducing battery lifespan.

Estimates of how long an e-bike battery will last vary and are dependent on other factors like the battery quality, but it’s typically suggested that you may need to replace your battery within three to nine years. 

It’s worthwhile taking steps to try to extend your battery’s life, as replacement batteries are expensive.

The bottom line...

You’ll see that there are many factors which influence your electric bike’s battery range and much you can do to increase it.

For many riders, as long as they keep their e-bike’s battery charged between rides, they’re unlikely to find range to be an issue. If your battery does give out on you before you’ve completed a ride, you can ride home unassisted so, unlike an electric car, you’re never going to be totally stranded by a flat battery.