"How long does the battery last?" is really two questions wearing the same coat. One is about a single charge — how far you can ride before you need an outlet. The other is about the pack itself — how many years before it stops holding a useful charge. Spec sheets answer the first question. They almost never answer the second, and the second is the one that eventually costs money.
Question one: how far on a single charge
A rated range on a spec sheet is a range, not a promise. Range varies with terrain and pedal-assist level, and also with rider and cargo weight, tire pressure, wind, temperature, and how much stop-and-go riding you do. A 20-mile day of steep hills on the highest assist setting is a completely different draw than 45 flat miles with light assist.
The practical move is to plan around the low end of the range, not the high end. If a bike is rated 30–45 miles and your round trip is 28 miles with hills, you are fine. If your round trip is 40 miles, you are relying on ideal conditions every single day.
One more piece of arithmetic worth knowing: capacity in watt-hours is volts times amp-hours. A 48V 15Ah pack is about 720Wh. A bigger pack does not translate into proportionally more miles, though, because a heavier bike or a hungrier motor pulls more energy per mile.
Question two: how many years
Lithium-ion packs age in two separate ways. Cycle aging comes from charging and discharging — every full cycle uses up a small slice of total capacity. Calendar aging happens just from time and storage conditions, even on a bike that sits in a garage untouched. Both show up the same way to a rider: the bike still works, but your usual ride now ends with less charge left than it used to.
Here is the honest part. Spec sheets almost never publish a cycle-life rating, so we are not going to invent a number of years for you. What is well established about lithium-ion chemistry in general is which conditions speed that fade up — and nearly all of them are within your control.
What actually shortens pack life
— Heat. Charging or storing a pack in a hot car, a sun-baked shed, or directly against a hot motor is the fastest way to age it. Battery temperature protection, where a pack has it, exists for exactly this reason, but no protection circuit makes a 110°F garage a good storage spot.
— Sitting at 0% or 100% for weeks. For long storage, a partial charge is easier on the cells than either extreme. Topping a pack to full right before it sits idle for a season is a habit worth breaking.
— Running the pack flat on every ride. Regular deep discharges are harder on cells than shallower, more frequent top-ups.
— Charging in freezing conditions. Bring a cold pack indoors and let it warm to room temperature before plugging it in.
— Using a mismatched charger. Each bike ships with a charger matched to its pack. A slower charge time is not a defect — it is the charger sized for that pack.
Habits that actually help
Charge indoors at room temperature, and unplug once the charge completes rather than leaving the bike on the charger for days. If your battery is removable, bring it inside in winter and in summer heat instead of leaving it on the frame outdoors. Keep tires at the pressure printed on the sidewall — underinflated tires quietly cost you miles. And if the bike will sit for a month or more, park it at a partial charge.
How to tell your pack is aging
Watch the ride, not the display. A gauge that drops faster than it used to, a shorter commute on the same route and assist level, or a pack that reaches full in markedly less time — these point to real capacity fade. One cold morning with short range does not; temperature alone moves range meaningfully.
Bottom line
Range on the sticker is a best case measured in ideal conditions. Plan around the low end of the rated range and you will rarely be surprised. Pack lifespan is not a fixed number anyone can quote you honestly, but the variables that decide it — heat, storage charge level, charger match, and depth of discharge — are all things you decide, every week, in how you park and plug in the bike.
If your range has dropped sharply or the bike won't power on at all, you can diagnose the problem step by step before buying any parts.