How Much E-bike Battery Capacity Do You Really Need?

So you’re looking to buy an electric bike and one of the most common questions is “how much battery capacity do I need?”

This can be a tricky question to answer because range depends on many factors. However, in this comprehensive guide, we’ll walk you through a simple yet effective process to figure out the right battery size for YOUR needs.

Key Factors That Determine E-bike Range

While manufacturers may provide estimates on expected range, real-world results can vary dramatically. The two biggest factors that impact e-bike range are:

1. Throttle vs. Pedal Assist

E-bikes come in two main types – throttle and pedal assist.

• Throttle e-bikes work like electric mopeds. You twist the throttle to engage the motor – no pedaling required.
• Pedal assist e-bikes amplify your pedaling power. The more you pedal, the more power the motor provides up to its maximum.

Throttle bikes drain the battery much faster than pedal assist. So when trying to determine range, you first need to know which type of e-bike you have.

2. Rider Input

The more human power through pedaling, the less battery power needed. A strong cyclist putting out lots of watts will get more miles from the same battery compared to a casual rider. Hills, headwinds, bike weight, tire pressure also impact efficiency and range.

So while my range estimates below are a good starting point, your specific results will vary based on your riding style and conditions.

Average E-bike Range in The Real-World

Based on my testing of dozens of e-bikes over thousands of miles, here are the average watt hours consumed per mile I’ve experienced:

• Throttle e-bike: 25 Wh/mi at 20mph
• Pedal Assist e-bike: 15 Wh/mi at 20mph

So for example, if you have a 500 Wh battery:

• On a throttle e-bike, 500Wh / 25Wh/mi = 20 miles of range
• On a pedal assist e-bike, 500Wh / 15 Wh/mi = 33 miles of range

These are for a 150 lb rider on relatively flat terrain with some gentle hills. Expect range to decrease as more challenging conditions enter the equation.

Let’s break down how you can customize these estimates for your specific situation.

Fine Tuning Range Estimates for YOU

While my averages above are decent guidelines, your exact watt hour per mile consumption will vary depending on your riding style, conditions, and e-bike setup. Here are the main factors to consider:

Rider Weight

Heavier riders use more battery power, lighter riders use less. However weight impacts range much more dramatically on hills than flat ground. To adjust for weight:

• Add 2-3 Wh/mi for every 50 lbs over 150 lbs
• Subtract 1-2 Wh/mi for every 50 lbs under 150 lbs

So my averages would increase by about 4 Wh/mi if I weighed 200 lbs instead of 150 lbs. And decrease by 3 Wh/mi at 100 lbs.

Terrain

Hills and headwinds decrease range substantially. Flat ground has minimal terrain impact.

• Add 3-8 Wh/mi for very hilly terrain
• Subtract 1-3 Wh/mi for very flat terrain

I ride in a area with rolling hills which is somewhere in the middle. Riding in the steep San Francisco hills may add 8+ Wh/mi to my baseline numbers. Conversely riding across the flats of central Texas could subtract 2 Wh/mi.

Level of Pedal Assist

If using pedal assist, your personal contribution matters tremendously.

• At the lowest assist levels, a strong rider can use ONLY 5 Wh/mi
• At the highest assist levels, a lazy rider may use over 25 Wh/mi

Most riders fall somewhere in the middle. I use levels 3-4 out of 5 which contributes to my 15 Wh/mi average.

E-bike Type

Heavier, less efficient e-bikes use more battery compared to lighter pedal-assist models:

• Add 1-4 Wh/mi for fat tire or cargo e-bikes
• Subtract 1-2 Wh/mi for lighter road e-bikes

So if I was riding a 60 lb cargo e-bike, I may add 3 Wh/mi over my standard pedal assist number. But if I switched to a featherweight 28 lb road e-bike I’d subtract 1 Wh/mi.

Speed

Faster speeds require more battery usage, lower speeds conserve energy:

• Every 5 mph over 20 mph adds 2-3 Wh/mi
• Every 5 mph under 20 mph subtracts 1-2 Wh/mi

I ride around 20 mph on average. Riding at only 15 mph could save me 3 Wh/mi. While full throttle at 25 mph may cost an additional 3 Wh/mi.

Calculate EXACT Ranges

Now let’s put this all together to calculate expected range based on YOUR specific situation.

First, establish your base watt hour per mile estimate from my averages:

• Throttle e-bike: 25 Wh/mi
• Pedal assist: 15 Wh/mi

Then adjust up or down based on your riding specifics – weight, hills, assist level, bike type, speed etc.

For example:

• You weigh 200 lbs (on a pedal assist bike)
• Mostly flat terrain
• Upper level assist (4 out of 5)
• Average speed 18 mph

1. Start with base of 15 Wh/mi
2. You weigh 50 lbs more than me. Add 3 Wh/mi.
3. Flat terrain. Subtract 2 Wh/mi.
4. Upper assist level. No change to base number.
5. 2 mph slower speed. Subtract 1 Wh/mi.

Total for you = 15 Wh/mi

Let’s say your potential e-bike has a 400 Wh battery. To calculate range:

• 400 Wh / 15 Wh/mi = 27 miles

It takes a bit of estimating at first. But after a few rides you’ll quickly hone in on your actual efficiency.

The key is to applicate real world factors to the baseline averages. This will get you in the ballpark. Then simply track your mileage and battery level over a few rides to dial in your specific watt hour/mile average.

Err On The Side Of More Battery

When trying to decide between two battery options, always opt for more rather than less capacity if possible.

You’ll likely ride further than you originally planned once you realize how fun riding an e-bike is! And there are few worse feelings than running out of juice before getting home.

Plus battery capacity plays a role in battery lifespan. All lithium batteries last longer with shallow vs. deep discharge cycles. So if your rides only use 50% of a large capacity battery, it will last many more charge cycles than heavily draining a small battery.

Finally, as batteries age they slowly lose capacity. More capacity now equals more usable range 3-5 years from now.

Range Anxiety is Overblown

Now that you know how to properly size your battery, you may be wondering: how frequently do I need to charge? How inconvenient will that be?

This concern about range and charging is known as “range anxiety”. And it’s both understandable for new e-bike owners, but also largely overblown.

Let’s look at some realities:

• Most e-bike trips are less than 7 miles. Even a small battery can easily handle this without charging.
• With just a standard wall outlet, batteries charge surprisingly fast – often completely full in 4 hours or less.
• Easy options exist for charging away from home like battery packs, solar panels, charging hubs etc.

There’s also the “80% rule” when sizing batteries:

Choose enough capacity so your average rides only use 80% or less of total range. This leaves 20% as a buffer for those times you ride further than normal. Sticking to 80% or less depth of discharge is better for battery health too.

So by using my guidelines to properly size your battery, and sticking to the 80% rule, you likely won’t have to charge after every use. Maybe every 2-3 days for most people. And when you do recharge batteries fill up quickly overnight.

This convenience helps eliminate most range anxiety concerns for new e-bike owners.

The Best “Upgrade” is Riding Efficiently

While a bigger battery will certainly give you more range, focusing on efficient riding is actually the best way to go further.

Let’s compare two riders with different riding styles on identical e-bikes:

• Rider 1 is a strong cyclist who pedals hard at the lowest assist level. He tips the scales at 130 lbs.
• Rider 2 relies heavily on throttle instead of pedaling. He weighs 230 lbs and rides aggressively at full speed.

Let’s plug in numbers assuming both e-bikes have a 400 Wh battery:

• Rider 1: 130 lbs, high pedal input, level 1 assist → 7 Wh/mi x 400 Wh capacity = 57 mile range
• Rider 2: 230 lbs, throttle-only, 25 mph → 30 Wh/mi x 400 Wh capacity = 13 mile range

That’s 4X more range for Rider 1 from the exact same 400 Wh battery!

Some key takeaways here on maximizing your miles:

• Pedal as much as comfortably possible
• Use lower assist levels when feasible
• Maintain slower speeds, avoid aggressive acceleration
• Consider weight reduction strategies if overweight
• Inflate tires properly, adjust brakes, lubricate drivechain

Focusing on efficiency is always the best way to save battery capacity and go further on your e-bike!

Key Things We Learned About E-Bike Range

• Real-world e-bike range depends on many individual factors
• Use my baseline Wh/mi estimates then customize for your specifics
• Opt for more battery capacity than less if possible
• Stick to ~80% maximum depth of discharge for best battery life
• Focus on riding efficiently to maximize miles from your battery
• Properly sizing your battery combined with occasional charges largely eliminates range anxiety concerns

I hope this guide gives you a practical process to determine the ideal battery size, expected range and charging needs for the way YOU plan to ride your new e-bike! Please let me know in the comments if you have any other questions.

Ride on!