E-Bike Battery Guide

Watt-hours is the only battery number worth comparing. Multiply the volts by the amp-hours and you have it: 36 V × 20 Ah is 720 watt-hours, and so is 48 V × 15 Ah. After that, three habits decide how long the pack lasts: charge it at room temperature, do not leave it sitting at 100 percent or at empty for weeks, and never charge it when it is below freezing. Do those and a good lithium pack should give you several hundred full charges before you notice it slipping.

Volts, amp-hours and watt-hours

Volts (V) is electrical pressure. A higher voltage system can deliver power to the motor more easily, which is why 48 V bikes often feel a little punchier off the line than 36 V bikes of the same wattage. It says nothing at all about how far you can go.

Amp-hours (Ah) is how much current the pack can supply for an hour. It only means something when you know the voltage it is supplied at. A 20 Ah pack at 36 V and a 20 Ah pack at 48 V are not the same size.

Watt-hours (Wh) is the actual energy stored, and it is the number that maps to distance:

volts × amp-hours = watt-hours

Pack	Watt-hours	Rough range at 12 Wh/km
36 V 10 Ah	360 Wh	about 30 km
48 V 10 Ah	480 Wh	about 40 km
36 V 20 Ah	720 Wh	about 60 km
48 V 20 Ah	960 Wh	about 80 km

Twelve watt-hours per kilometre is a middling real-world figure for a standard 500 W hub bike. The full explanation of where that number comes from, and how to work out your own, is in how far can an e-bike actually go.

If a listing gives you volts and amp-hours but never watt-hours, do the multiplication before you compare prices. It is the single most useful thirty seconds of e-bike shopping there is.

What is actually inside the pack

An e-bike battery is not one big cell. It is dozens of small cylindrical lithium-ion cells, usually the 18650 or the larger 21700 size, wired in series to make the voltage and in parallel to make the capacity. Cell quality is most of what separates a good pack from a cheap one, and it is invisible from the outside.

Every proper pack also contains a battery management system, the BMS. It is a small circuit board that stops any cell being overcharged or run flat, keeps the cells balanced with each other, cuts the output if the current gets too high, and in better packs refuses to charge when the cells are too cold. The BMS is why you should only ever use the charger built for your pack. A charger that does not talk to the right BMS is not a bargain.

Charging habits that make a pack last

• Charge indoors at room temperature. Somewhere between about 10 and 25 °C is ideal. A removable pack means you can bring it in, and you should.
• Never charge a pack below 0 °C. Charging a frozen lithium cell plates metallic lithium inside it, and that damage does not come back. Let a cold pack sit indoors for an hour or two before you plug it in. This is the one rule that actually kills batteries in Canada.
• Do not leave it on the charger for days. Unplug it when it is done. A pack sitting at a full 100 percent for weeks ages faster than one sitting at half.
• Charging to 100 percent is fine when you are about to ride. If the bike is going away for a month, take it down to somewhere around half instead.
• Do not run it flat over and over. Deep discharges are harder on cells than shallow ones. Topping up after most rides is better for the pack than draining it every time.
• Charge on a hard surface, not on a couch, a bed or a pile of rags, and not blocking the only way out of a room. Lithium fires are rare and they are serious.
• Never charge a pack that is swollen, cracked, or has been in a crash or under water. Get it looked at.

Use the charger that came with the bike, or a proper replacement for it. We stock the correct charger for the X1 so you do not end up guessing at a generic one, and it is cheap enough to keep a second one at work.

Storing a battery over the winter

Most Canadian e-bikes sleep for four or five months a year, and how they sleep matters more than most owners realise.

• Take the pack off the bike and bring it inside. An unheated garage or shed at minus 25 is not a storage place.
• Store it at roughly 50 to 60 percent charge, not full and not empty. A pack left flat all winter can drop below the voltage the BMS will let you recharge from, and at that point it is scrap.
• Somewhere cool, dry and above freezing. A basement shelf is close to perfect. Not beside the furnace, not in direct sun.
• Check it every couple of months and top it back up to about half if it has drifted down.

If you ride through the winter instead of storing the bike, read winter riding in Canada, which covers the cold-weather range loss and what to do about it.

How long should a battery last?

Lithium-ion packs are usually rated in charge cycles, where one cycle is a full charge worth of energy however it was used. Good cells are generally quoted at several hundred cycles, commonly in the region of 500 to 1,000, before the pack settles at about 80 percent of its original capacity. For most riders that works out to somewhere in the range of three to six years of ordinary use.

Note what "worn out" means here. It does not mean the pack stops. It means your 60 km ride is now a 48 km ride. Batteries fade rather than fail, and calendar age matters as well as use, which is why a five year old pack that has barely been ridden is still a five year old pack.

Signs a pack is on its way out

• Range has dropped a lot and stayed dropped, in mild weather, not just in the cold.
• The gauge falls off a cliff near the end instead of coming down steadily.
• It charges much faster than it used to, which means there is less in there to fill.
• It gets noticeably warm sitting on the charger.
• The case has swollen or the pack rattles. Stop using it.

A tired pack is a replacement job, not a repair job for most people. A spare 20 Ah battery uses the same mount and the same key, so it is a five minute swap, and having a second one also doubles your range on long days. Everything else that wears is in parts and accessories.

Recycling an old pack

Lithium batteries do not belong in household garbage or in a blue box, and dropping one in a garbage truck is how truck fires start. Call2Recycle runs battery collection across Canada. Check their site for a drop-off location near you that accepts e-bike packs, since not every location takes the large ones. Municipal hazardous waste depots often take them as well.

Buying advice in one paragraph

Compare watt-hours, not volts. Ask whether the pack comes off the frame. Ask what a replacement costs today and whether you will be able to buy one in three years, because that answer tells you whether you are buying a bicycle or an appliance with an expiry date. The X1 specifications list the pack we use, and the buying guide covers the rest of the bike.

Read next

• How far can an e-bike actually go?
• Winter riding in Canada
• Electric bike buying guide