Electric Bike Batteries Explained

The short version

Watt-hours is the number that matters. Volts times amp-hours gives you watt-hours, and watt-hours is the only figure that lets you compare a 36V bike against a 52V one honestly.

A 48V 15Ah pack and a 52V 14Ah pack sound different and are nearly identical: 720Wh against 728Wh. Manufacturers know which of the two numbers flatters them, and quote accordingly.

Volts, amp-hours, watt-hours

Voltage is roughly how hard the pack can push. Higher voltage systems deliver the same power at lower current, which means less heat and less loss in the wiring. Voltage is a design choice rather than a quality tier: the premium mid-drive systems from Bosch, Shimano, Yamaha and Brose run at 36V, while most direct-to-consumer hub-motor bikes use 48V or 52V. Compare packs on watt-hours instead.

Amp-hours is how much charge the pack holds, but only at its own voltage. Comparing amp-hours across bikes of different voltages is meaningless.

Watt-hours is the total energy stored, and it is the honest one. Multiply volts by amp-hours:

Turning watt-hours into miles

A rider on moderate assist typically draws 10 to 20 watt-hours per mile. Divide the pack size by your figure and you have a realistic range, which will usually be well short of the marketing claim.

A 720Wh battery at 15Wh per mile is 48 miles. The same bike advertised at 65 miles is not lying — it is quoting the lowest assist setting, a light rider and flat ground.

What pushes consumption up: hills, headwinds, cold weather, low tire pressure, a heavier rider, cargo, stop-start riding, and throttle use instead of pedal assist. Cold is the one people forget. Below freezing, expect to lose 20 to 30% of usable capacity until the pack warms up.

Chemistry: what e-bikes actually use

Almost every e-bike pack is lithium-ion NMC, not the LiFePO4 you find in a good power station. NMC is far lighter for the same energy, which matters enormously on a bike and not at all on something that sits in a cupboard.

The trade is lifespan. NMC e-bike packs are typically rated for 500 to 1,000 full charge cycles, where LiFePO4 manages several thousand. A few brands now offer LiFePO4 e-bike packs; they last longer and weigh noticeably more. Our LiFePO4 vs lithium-ion guide covers the difference in full.

Making a pack last

The habits that matter, in order of how much difference they make:

Avoid both extremes

Charging to 100% and sitting there is hard on a lithium pack, and so is running it to zero. If your charger or app supports an 80% or 90% limit, use it for daily riding and charge full only before a long trip.

Store it at about half charge

For anything over a few weeks, leave the pack near 50% and top it up every couple of months. A battery stored full ages faster; one stored empty can drop below the voltage the protection circuit will accept, which kills it outright.

Keep it out of the cold

Never charge a pack below freezing — that is what causes lithium plating and permanent damage. Bring it indoors, let it reach room temperature, then charge.

Use the charger it came with

CPSC’s advice is to use only the charger supplied with the bike or one its maker recommends. That matters most when you buy a spare pack later: Lectric’s spare batteries, for example, ship in a separate package without a charger, so check that the one you plug in is a model the maker lists for that pack.

How many years a pack lasts

A charge cycle means using 100% of the pack’s capacity, not one trip to the charger. Two rides that each use half the battery count as one cycle. Aventon’s battery guide puts a quality lithium-ion e-bike pack at 500 to 1,000 full charge cycles, or three to five years.

Because partial charges count as fractions, you can work out how long it would take to use up the cycle rating. At 15Wh per mile, a 12-mile round trip on flat ground takes about 180Wh, roughly a quarter of a 700Wh pack. Five rides a week is 260 rides a year, or about 67 full cycles.

For most commuters, then, the cycle rating is not what retires the pack. Age and heat are. Aventon notes that heat speeds up chemical aging inside the cells, that the capacity lost that way does not come back, and that packs stored or charged above roughly 90°F, or left in freezing temperatures, degrade faster. Treat the cycle rating as a ceiling; the habits above decide how close you get to it.

Aventon’s own battery warranty is shorter than either figure: two years from purchase or 300 charging cycles, whichever comes first. A pack that fades after that is a replacement you pay for.

Replacement and certification

A replacement pack typically runs $300 to $700, which is a real part of the cost of ownership. Lectric’s spare-battery list shows the spread:

All four are listed as certified to UL 2271, and each fits only named models. The two 840Wh packs hold the same energy and are $125 apart, but they are not interchangeable: one fits the XP4 750 Step-Thru, the other the XPedition 2.0 and XP Trike2 750. The XP4 packs do not fit the older XP 1.0 to 3.0 because the key position changed. The price that matters is the one for your exact model.

Before buying a bike, check the manufacturer still sells the pack — some cheaper brands orphan a model after a couple of years and leave owners with a bike they cannot re-battery.

Buy the manufacturer’s own pack, or one it confirms for your bike. CPSC’s guidance is to use only a replacement battery that has been tested and approved to work safely with your device, and never a pack modified or reworked by unqualified people. Rules vary by city and state: New York City, for example, bars the sale, lease or rental of e-bikes not certified to UL 2849 and batteries not certified to UL 2271 (Local Law 39 of 2023). That law covers selling and renting, not where you charge; rules on charging or storing a battery indoors mostly come from landlords, building owners and local fire codes, so check your lease or building rules.

Charging safety, recalls and disposal

CPSC’s battery guidance for e-bikes and other micromobility products comes down to a few habits:

• Stay with it while it charges. Don’t charge while you are asleep or away from home. CPSC says it has seen many lithium-ion battery home fires and deaths happen at night while batteries were charging.
• Check for recalls. CPSC lists e-bike recalls on its Micromobility Information Center. If your battery or bike is under a recall or product safety warning, follow the disposal instructions in CPSC’s recall notice.
• Report problems. If you have an issue with a pack, report it to CPSC at SaferProducts.gov.

A dead pack never goes in the trash or the curbside recycling bin. Take it to a battery recycler or a household hazardous waste collection site. To prevent fires, the EPA says to cover the terminals with non-conductive tape such as electrical tape and to put the battery in its own plastic bag. If the pack is damaged, contact the maker for specific handling information. EPA also points to retailers that run battery take-back services, so ask whether the shop that sold the bike will take the pack.