Lithium ion electric e bike battery pack

How an e-bike pack is specified

The pack is the heaviest and most expensive single component on an e-bike, and it is the one most often specified by habit rather than by calculation. Three parameters determine everything else, and they are related — change one and the others move.

Voltage follows from the chemistry and the S count: 18650 and 21700 cells run at 3.6V to 3.7V nominal, so 10 cells in series give 36V, 13 give 48V, 14 give 52V and 20 give 72V. Capacity follows from the P count — a 13S4P pack has four cells in parallel in each of the thirteen series groups, which multiplies both the amp-hours and the deliverable current by four.

Voltage classes and what they suit

Voltage is not a free upgrade. The controller defines the maximum the system will accept, and raising the pack voltage above it risks damaging the controller and the motor. Where a rider wants more from a 48V system without changing hardware, the common route is the 52V variant, which stays within the tolerance of most 48V controllers.

Sizing voltage, capacity and current together

Start from the motor. Divide its rated power by the pack voltage to get the continuous current, then add headroom for peak draw and controller losses. A 750W motor on a 48V pack draws roughly 16A continuous, so a 30A BMS gives comfortable margin; a 1,500W motor draws about 31A and needs a 40A to 50A BMS. Underspecifying the BMS is the most common cause of a pack that shuts down under load.

Then size capacity from range. Amp-hours multiplied by nominal voltage gives watt-hours, and watt-hours divided by the bike’s consumption — typically 15Wh to 25Wh per kilometre depending on rider weight, terrain and how much the rider pedals — gives the range. A 48V 15Ah pack is 720Wh and delivers roughly 30km to 45km on a mixed route.

Cells and casing

We build primarily from 18650 cells, with 21700 and 26650 where the housing permits — 21700 gives higher capacity per cell and fewer interconnections, at the cost of a slightly larger enclosure. Cells come from the mainstream manufacturers in this market, and where a customer has a preferred part number we will build to it.

Case availability is a real constraint. The standard formats are cheap because the tooling is amortised across large volumes; an unusual shape is a tooling project with a lead time and a minimum order, not a catalogue item. In practice most custom work is a standard case with a raised capacity, which is why custom builds usually hold a standard housing and a non-standard cell configuration.

The BMS

Every pack we build carries a BMS with cell balancing and protection against over-charge, over-discharge, over-current, short circuit and over-temperature. Beyond those basics, the specification depends on the bike: communication over CAN or UART where the controller expects it, Bluetooth monitoring where the rider wants a phone app, and a temperature sensor close to the cells where the pack is enclosed and high-draw.

Certifications

• UN38.3 — mandatory transport test; required for every cross-border shipment.
• UL 2849 — the North American standard for e-bike electrical systems.
• EN 15194 / EN 50604 — the European e-bike and light-EV battery standards.
• IEC 62133 — baseline safety standard for portable sealed lithium cells and packs.
• KC (Korea) and PSE (Japan) — market-specific access requirements.

What determines the cost

Four things move the price of an e-bike pack: the cell, because a high-drain branded cell costs materially more than a commodity one; the capacity, which is a direct function of cell count; the casing, and whether it is a stocked format or a new tooling; and the BMS specification. Send the voltage, capacity, cell preference, housing and motor rating to our RFQ page and we return a quotation against all four.

E-bike battery FAQ

What voltage e-bike battery do I need?

Match the motor and controller: 36V for 250–500W motors, 48V for 500–1,500W, 52V as a 48V upgrade for more speed and torque, and 72V for high-performance and light-EV applications. The controller defines the maximum, so confirm it before choosing a pack.

How do I calculate the current the BMS must handle?

Divide the motor’s rated power by the pack voltage, then add headroom for peak draw and controller inefficiency. A 750W motor on a 48V pack draws roughly 16A continuous, so a 30A BMS gives comfortable margin. Undersizing the BMS is the most common cause of a pack shutting down under load.

What cells do you build e-bike packs from?

Primarily 18650, with 21700 and 26650 where the housing permits. We build with the mainstream cells in this market — Samsung, LG, Panasonic, Sony and Molicel — and will build to your specified cell if you have a preferred part number.

What is the difference between 10S, 13S and 14S packs?

The S number is the count of cells in series, which sets the nominal voltage: 10S is 36V, 13S is 48V, 14S is 52V. The P number is the cells in parallel, which sets capacity and the continuous current the pack can deliver. A 13S4P is a 48V pack with four cells in parallel per series group.

Can you build a replacement pack for a discontinued e-bike?

Yes. Send the original pack or a dimensioned drawing with the connector and mounting arrangement, along with the motor rating and the charger specification, and we build to that envelope.

What housing formats are available?

Down-tube, rear-rack, and the common ‘frog’ and ‘hailong’ case styles, along with custom shapes. Case availability constrains what can be built off the shelf; an unusual shape is a custom-tooling project rather than a catalogue item.

Does the pack include a BMS?

Every pack we build has a BMS with cell balancing and protection against over-charge, over-discharge, over-current, short circuit and over-temperature. Where the application needs it we add communication — CAN or UART — or Bluetooth monitoring.

What certifications apply to e-bike batteries?

UN38.3 for transport is mandatory and applies to every cross-border shipment. Depending on the target market, expect UL 2849 (North America, e-bike electrical systems), EN 15194 / EN 50604 (Europe), KC (Korea), PSE (Japan) and IEC 62133 as the baseline cell and pack safety standard.

Explore related pages

• Custom lithium battery pack projects
• Power tool replacement batteries
• 14.4V and 14.8V 4S lithium-ion packs
• 18650 pack calculator
• Custom battery pack design
• Wholesale batteries

Request an e-bike battery quote

Send the motor rated power, the controller maximum voltage, the required range, your preferred cell, the housing format and the annual volume — we confirm the configuration before quoting.