How to Choose an E-Bike Battery: Voltage, Capacity, Casing [2026]
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Replacing the battery in an e-bike is usually the single most expensive decision in that vehicle's whole life. It's also the one where it's easiest to make a mistake you can't undo — because a battery bought for the wrong standard simply won't work.
The good news: there are only a few numbers you actually need to check.
Four parameters to start with
- Voltage (V) — must match the controller. No room for compromise here.
- Capacity (Ah) — determines range.
- Continuous current (A) — must cover the motor's demand.
- Casing and mounting — determines whether the battery physically fits the frame.
The order isn't arbitrary. The most common mistake looks like this: the customer starts with the casing ("I want the same one I had"), and ends up buying a battery whose voltage doesn't match the controller.
Voltage: 36 V, 48 V, 52 V — and why you shouldn't guess
A Li-Ion battery's voltage comes directly from the number of cells connected in series. A single lithium-ion cell has a nominal voltage of roughly 3.6–3.7 V and a maximum of 4.2 V when fully charged.
| Configuration | Nominal voltage | Voltage at full charge |
|---|---|---|
| 10S | ~36 V | 42 V |
| 13S | ~48 V | 54.6 V |
| 14S | ~52 V | 58.8 V |
The controller has programmed voltage thresholds. A 52 V battery connected to a 36 V controller will usually damage it immediately. Going the other way — a 36 V battery in a system designed for 48 V will run briefly and weakly, then drop below the cutoff threshold.
You'll find the voltage on the old battery's label or on the controller itself. If the label is unreadable and you can't find the bike's spec — message us before ordering. That's five minutes of correspondence instead of a burned-out controller.
Capacity: converting amp-hours into kilometres
Amp-hours (Ah) alone don't tell you much until you combine them with voltage. The real measure of energy is the watt-hour:
Wh = nominal voltage (V) × capacity (Ah)
A 48 V 21 Ah battery holds roughly 1000 Wh of energy.
An average e-bike uses 10–25 Wh per kilometre. The spread is wide because consumption depends on the weight of the bike and rider, terrain, tyre pressure, ambient temperature, and — most of all — how much you pedal yourself. A bike on the lowest assist level on flat terrain will land at the low end. The same bike on throttle, uphill, with a heavier rider — at the high end.
That gives a practical rule of thumb: a 1000 Wh battery is realistically 40–100 km. Anyone who quotes a single precise number without these caveats is selling marketing, not data.
Casing: Hailong, Shark, bottle-style, dedicated
Casing standards developed around how the battery mounts to the frame. Four you'll run into most often:
| Casing type | Mounting | Characteristics |
|---|---|---|
| Hailong | Down tube, mounting rail | The most common market standard; wide availability, straightforward install |
| Shark | Down tube, mounting rail | Narrower and more compact than Hailong; looks better on slim frames |
| Bottle-style | In place of a bottle cage | Most universal for unusual frames; easy to remove and carry |
| Dedicated | For a specific bike model | E.g. packs for Duotts C29 / M29 / C26 / M26 — fit only their own model |
Practical note: dimensions and rail spacing can vary between manufacturers even within the same "standard." Before ordering, measure the length, width and height of the old casing and the spacing of the mounting holes on the frame. A photo of the battery next to a tape measure, sent to us, usually settles this in one message.
The cells inside: not a minor detail
Two batteries with identical numbers on the label can differ by hundreds of life cycles — because they contain completely different cells inside.
Branded cells (Samsung SDI, LG, EVE) have documented characteristics: known real-world capacity, known continuous current rating, predictable degradation curve. Unbranded cells from an uncertain source have a number printed on the wrapper that doesn't always match reality.
The split is simple. High-capacity cells (Samsung 35E, Samsung 53G, LG M58T) give more range at moderate current draw. High-current cells (Samsung 30Q, Samsung 50S, EVE 40P) deliver more power at the expense of capacity. For a bike with 250–500 W assist, capacity matters most; stronger drives need current headroom.
We've covered this in detail in two dedicated comparisons: Samsung 35E vs 30Q vs LG M29 for the 18650 format, and Samsung 53G vs 50E vs 50S vs LG M58T for 21700. If you're weighing up the formats themselves, we also have a 18650 vs 21700 guide with calculations.
Charger: 3 A or 8 A
A standard 48 V charger runs at 2–3 A and charges a ~20 Ah pack in about 7–8 hours. A fast 8 A charger cuts that down to 2.5–3 hours.
Fast charging has a cost: higher current means higher cell temperature, and temperature is the main factor that accelerates degradation. If the bike sits in a garage overnight, a 3 A charger is simply the better choice for pack longevity. An 8 A charger makes sense where the bike works during the day and needs to be back in service on a break — couriers, rental fleets, back-to-back commutes with no downtime.
Three rules regardless of charging current:
- The charger's output voltage must match the battery's maximum voltage: 42 V for a 36 V pack, 54.6 V for 48 V, 58.8 V for 52 V.
- The connector must match — usually DC 5.5×2.1 mm or XT60. Check the type before ordering, not after.
- For winter storage, charge the pack to around 60% and keep it at room temperature. A battery left discharged in the cold is the most common cause of "my battery won't wake up in spring" complaints.
Checklist before you order
Before you click "buy," write down five things:
- Voltage of the old battery or the controller (36 / 48 / 52 V)
- Motor power in watts — from the label on the motor
- Dimensions of the old battery and the spacing of the mounting holes
- Connector type — power and charging, separately
- Real range requirement — the longest route you actually ride, plus a 30% margin
With these five numbers, choosing a battery stops being guesswork.
If any of them is unclear — get in touch. We answer technically, not with a sales pitch: if nothing in our range fits your bike, we'll tell you straight.
Ready-made packs are in our e-bike batteries collection. If you're building a pack yourself or rebuilding an old one, we carry 18650 cells and 21700 cells from Samsung, LG, EVE and BAK.
Frequently asked questions
Will a 52 V battery work in a bike built for 48 V?
Sometimes, but it depends entirely on the controller. Many 48 V controllers accept 52 V because their upper threshold has headroom built in — but some don't. Higher voltage mainly means more power and speed, not more range. Without confirmed controller specs, it's a risk that isn't worth taking for a few percent more power.
How many cycles does an e-bike battery last?
Branded Li-Ion cells retain around 80% of their original capacity after 500–800 full charge cycles, under normal use and avoiding deep discharge. In practice, that's several riding seasons. Degradation speeds up with regular charging to 100% combined with discharging to zero, and with operation at high temperatures.
Why has my range dropped even though the battery seems fine?
Natural capacity fade is one reason, but usually not the only one. Check tyre pressure, ambient temperature (range drops 20–30% in winter and recovers in spring), the assist level you're using, and the weight you're carrying. If the drop is sudden and large, the cause is often a single weak section of the pack rather than the whole battery — worth diagnosing before you replace the entire thing.
What's the difference between Hailong and Shark casings?
Mainly geometry. Shark is narrower and more compact, which makes it look better on slim frames and fit where Hailong doesn't. Hailong is more widely used and more often the one being replaced with a new pack. Both mount on a rail on the down tube.
Can I use my old charger with a new battery?
Only if the output voltage matches, the current doesn't exceed what the new pack allows, and the connector fits. Check the voltage on the charger's label — it should match the battery's maximum voltage (42 / 54.6 / 58.8 V), not the nominal one.