The short answer
Choose the battery system voltage that matches your motor and controller — not the biggest number available. As a rule of thumb: 12V for lights, toys and small backup; 24V for scooters and medical equipment; 36V for entry e-bikes (EU 250W class); 48V for mainstream e-bikes, power tools and robotics; 72V and above for high-power e-motos and heavy robotics. Voltage is set by the device’s controller, so the battery must match the system, not the other way round.
How battery voltage is determined
A lithium pack is built from cells in series. With a nominal 3.6–3.7V per NMC cell (3.2V for LiFePO4), the pack voltage is the number of cells in series multiplied by the cell voltage. A 13S NMC pack is 13 × 3.7V ≈ 48V nominal; a 20S pack is ≈ 72V. This is why “48V” and “72V” are really statements about the series count, and why the motor controller’s input range fixes the voltage before anything else is designed.
Voltage tiers and typical applications
| System | Series count (NMC) | Typical applications |
|---|---|---|
| 12V | 3S–4S | LED lighting, toys, small backup, accessories |
| 24V | 6S–7S | E-scooters, electric wheelchairs, medical equipment, small robots |
| 36V | 9S–10S | Entry e-bikes (EU 250W), electric cargo trikes, light tools |
| 48V | 13S–14S | Mainstream e-bikes, power tools, delivery bikes, small robots |
| 72V+ | 20S+ | E-motos, high-power e-bikes, humanoid and industrial robots, AGVs |
Why you cannot just “pick a higher voltage”
Higher voltage means more power for the same current — but the motor and controller are built for one window. Running 72V into a 48V controller destroys the controller; running 48V into a 72V system under-performs. In custom projects the sequence is:
- Define the motor’s power requirement and the controller’s input range.
- Select the series count (S) that lands inside that range.
- Size the parallel count (P) and cell format for the required capacity (Ah) and discharge current.
- Choose the BMS rated for the pack voltage and the peak current.
For example, a 48V 15Ah e-bike pack at 13S with 21700 NMC cells and a 30A continuous BMS covers a 500–750W motor comfortably — that is the configuration of our 48V 15Ah e-bike battery case study. A 41.2V humanoid robot pack (Samsung 50S cells, 150A max discharge, RS485 + Bluetooth) shows how a non-standard voltage follows the controller of the robot.
Voltage, capacity and C-rate work together
Three numbers define a pack: voltage (V), capacity (Ah) and maximum discharge current (A, or C-rate). Energy is V × Ah in watt-hours. A 48V 20Ah pack holds 960Wh; a 36V 20Ah pack holds only 720Wh at the same Ah — which is why comparing packs by Wh rather than Ah avoids costly mistakes. And the C-rate (current relative to capacity) decides whether the pack can deliver the motor’s peak draw without sagging or overheating. Our maximum discharge current article covers C-rate in depth.
Voltage & chemistry: NMC vs LiFePO4
LiFePO4 cells have a lower nominal voltage (3.2V) than NMC (3.6–3.7V). A “48V” LiFePO4 pack therefore needs 15S or 16S, and its charge curve (3.2–3.65V per cell) must match the controller’s window. If you are replacing an NMC pack with LiFePO4 in an existing system, verify controller compatibility first — some systems accept it, others cut off early. See Li-ion vs LiFePO4 for the chemistry comparison.
Frequently asked questions
What voltage battery do I need for a 500W e-bike motor?
36V or 48V both work for 500W, depending on the controller. 48V is the most common choice for mid-drive and cargo builds because it delivers the same power at lower current, reducing wiring and heat.
Is a 52V battery the same as 48V?
Not exactly. “52V” usually means a 14S pack (58.8V full charge) versus 13S for standard 48V (54.6V). Only use it if the controller explicitly supports 14S input.
Can I change the voltage of my battery pack later?
Only with a redesign: the series count is fixed by the controller, and changing it changes the BMS, charger and often the physical layout. This is why defining the system voltage early in a custom project matters.
What voltage do industrial robots use?
Depends on the platform. Our 41.2V humanoid robot pack is a custom voltage chosen to match the robot’s servo controller; AGVs often run 24–48V, large industrial robots 48–96V. Share your controller spec and we will size the pack.
Unsure which voltage fits your device?
Send the motor/controller specs and your space constraint via the custom battery inquiry form — our engineers will propose the series count, cell format and BMS in the first reply.
Chemistry changes the voltage ladder
All voltage classes above assume NMC lithium-ion cells at 3.6–3.7V nominal. LiFePO4 cells sit at 3.2V nominal (3.65V full charge), so the same nominal pack voltage needs a different series count: a “48V” LiFePO4 pack is 15S or 16S, not 13S. Never swap chemistries without re-calculating the series count, the BMS parameters and the charger — a 13S LiFePO4 pack is closer to 40V and will not run a 48V controller correctly. Read our Li-ion vs LiFePO4 guide for the full comparison.
Voltage, current and the charger
The pack’s nominal voltage tells you only part of the story. Under load, every pack sags: internal resistance drops the terminal voltage in proportion to current, which is why a weak or cold pack trips its low-voltage cutoff under acceleration even when the label voltage looks correct. The charger must also match the pack’s full-charge voltage and charging profile — a 48V NMC pack charges to 54.6V (13S × 4.2V), while a LiFePO4 equivalent charges to 54.4V (16S × 3.4V) or 54.75V depending on the BMS spec. Charging with the wrong profile either under-charges (lost range) or risks over-voltage protection trips.
When a device lists a voltage range (for example 36–54.6V input), it usually means the controller accepts that full range, and the battery’s nominal voltage should sit comfortably inside it. If in doubt, share the controller specification with your supplier together with the battery enquiry — matching voltage, connector and communication in one pass saves weeks later.