# 36 V vs 48 V e-bike batteries Source: https://pedalandvolt.co.uk/blog/36v-vs-48v-ebike-battery Published: 2026-10-12 Publisher: Pedal and Volt **In short:** A 48 V battery is not automatically more powerful, faster or less legal than a 36 V one. Power depends on voltage and the current the controller allows, and range depends on watt-hours (volts x amp hours). Legality in the UK depends on the motor's 250 W continuous rating and the 15.5 mph assist cut-off, not on voltage. The key rule is to match the battery voltage to your motor and controller, and never swap a 36 V system to 48 V without the maker's approval. Battery listings lead with voltage, so it is easy to assume a 48 V pack is better than a 36 V one. In practice voltage is just one part of the picture. What matters for range is energy in watt-hours, what matters for power is the whole system, and what matters for your bike is that the battery matches its controller and connector. This guide explains each point and compares three replacement packs from our guide. ## Volts, amp hours and watt-hours Voltage is the electrical pressure the pack supplies. Amp hours (Ah) describe how much charge it holds. Multiply the two and you get watt-hours (Wh), which is the energy available and the best single guide to range. A 36 V 14 Ah pack holds 504 Wh. A 48 V 13 Ah pack holds 624 Wh. A 36 V 15.6 Ah pack holds about 562 Wh. So a 48 V pack only has more energy if its Wh figure is higher. Compare Wh, not volts. Our [battery and charge cost tool](https://pedalandvolt.co.uk/tools/battery-and-charge-cost) calculates Wh, cost per charge and estimated range. ## Three packs from our guide These figures come from the sellers' listings. The Wh values are worked out from the listed volts and amp hours, apart from the Xiseny, which lists 504 Wh. | Spec | Xiseny 36 V 14 Ah | SDTYYP Silverfish 36 V 15.6 Ah | FEIMOKY HL-4813UK 48 V 13 Ah | | --- | --- | --- | --- | | Voltage | 36 V | 36 V | 48 V | | Capacity | 14 Ah | 15.6 Ah | 13 Ah | | Energy | 504 Wh (listed) | About 562 Wh | About 624 Wh | | Max continuous discharge (BMS) | 15 A | 30 A | 30 A | | Mount | Integrated tube style | Silverfish (XH370-10J) | Hailong | | Connectors | 2-pin discharge, DC 2.1 charge | 2-pin discharge, XLR charge | Not stated | | Certification stated | CE, RoHS, UN38.3 | CE, RoHS, UN38.3 | UKCA, CE | Listed specs of three replacement batteries ## Does 48 V mean more power or speed? Power in watts equals volts times amps. A controller limits the current it draws, so a 48 V system can deliver the same power as a 36 V one at lower current. Higher voltage can make a motor feel a little livelier at higher pedalling speeds, but on a UK e-bike the controller still stops assisting at 15.5 mph, so top assisted speed does not change. Lower current at 48 V means slightly less heat in wiring and connectors for the same power. That is one reason some makers choose it. But a well-designed 36 V system is perfectly capable on a 250 W bike. ## Voltage and UK law The EAPC rules look at the motor's continuous rated power (250 W) and the assist cut-off speed (15.5 mph, 25 km/h). Voltage is not a legal limit. The EAPC plate may show the battery voltage, but a 48 V pack on a 250 W motor with the right speed limit is as legal as a 36 V one. See [EAPC plate markings](https://pedalandvolt.co.uk/blog/eapc-plate-markings) and check gov.uk for the rules in force. Be wary of listings that pair a 48 V battery with 750 W or 1000 W motors. It is the motor rating that takes those bikes outside the rules, as our [off-road only guide](https://pedalandvolt.co.uk/blog/off-road-only-ebikes-explained) explains. ## Matching a battery to your bike Your controller is built for a specific voltage. Fitting a 48 V battery to a 36 V controller can damage the controller and display, and may create a safety risk. Fitting a 36 V battery to a 48 V system will usually trip the low-voltage cut-off or not work at all. Match the voltage exactly unless the bike maker says otherwise. Next, match the mount style, the discharge connector, the charge port and the physical size. The BMS discharge limit should meet or exceed what your controller draws. Finally, use the charger made for that battery: a 36 V pack charges to 42 V, a 48 V pack to about 54.6 V, and chargers are not interchangeable. 1. Read the voltage on your current battery or the controller label. 2. Measure the battery and photograph the mount and connectors. 3. Check the controller's current rating against the new battery's BMS limit. 4. Buy a pack with the same voltage, mount and connectors. 5. Use the charger supplied with the new battery. Note: Lithium batteries store a lot of energy. Use only the charger supplied for that battery, charge where you can keep an eye on it, and stop using a pack that is damaged, swollen or unusually hot. Never open a battery or change the system voltage without the maker's approval. ## Which to choose Buy the voltage your bike already uses. Within that voltage, choose the highest Wh that fits your mount if you want more range, and check the BMS current suits your controller. If you are building a conversion, both 36 V and 48 V 250 W kits are common; pick a well-supported kit and buy the battery to match. Our [replacement e-bike battery guide](https://pedalandvolt.co.uk/best/best-ebike-replacement-batteries) compares packs by voltage, mount and stated certification. [Compare replacement e-bike batteries](https://pedalandvolt.co.uk/best/best-ebike-replacement-batteries) ## Frequently asked questions **Can I use a 48 V battery on a 36 V e-bike?** Not without the maker's approval. The controller and display are built for 36 V and may be damaged. **Is 48 V faster than 36 V?** Not on a UK EAPC. The controller stops assisting at 15.5 mph whatever the voltage. **Does 48 V give more range?** Only if the pack has more Wh. Compare watt-hours rather than volts. **Is a 48 V e-bike legal in the UK?** Yes, if the motor is rated at 250 W continuous and assistance cuts out at 15.5 mph. ## Buying guides on this topic - https://pedalandvolt.co.uk/best/best-ebike-replacement-batteries - https://pedalandvolt.co.uk/best/best-long-range-electric-bikes ## Sources - [gov.uk: Electric bikes, licensing, tax and insurance](https://www.gov.uk/electric-bike-rules)