E-bike battery listings are full of numbers — 36V, 48V, 13Ah, 20Ah — that can be confusing if you're buying your first replacement or upgrade. Here's what they actually mean and how to use them to choose the right battery.
Voltage (V): how it affects power
Voltage is a rough indicator of how much power a battery can deliver to the motor. Common e-bike voltages are 36V, 48V and 52V. Higher voltage generally means stronger acceleration and better hill-climbing for a given motor, which is why higher-power bikes and conversion kits tend to use 48V or 52V systems. Voltage isn't interchangeable between systems — a battery must match what your motor and controller are designed for, or it simply won't work (and in the wrong combination, could damage the system).
Amp-hours (Ah): how it affects range
Amp-hours describe the battery's storage capacity — essentially, how much charge it holds. A higher Ah rating at the same voltage means more range between charges, all else being equal. A 48V 20Ah battery stores roughly 50% more energy than a 48V 13Ah battery, so you'd expect noticeably more range from it, though real-world range always depends on rider weight, terrain, tyre type, and how much you rely on the throttle versus pedal assist.
Watt-hours (Wh): the number that lets you compare fairly
Because voltage and Ah both affect range, the fairest way to compare two batteries is watt-hours, calculated as voltage × amp-hours. For example, a 48V 13Ah battery is 624Wh, while a 36V 20Ah battery is 720Wh — despite the lower voltage, the second battery actually stores more energy. When comparing batteries across different voltage systems, always check Wh rather than Ah alone.
Battery placement: downtube, rear rack and triangle
E-bike batteries come in a few common shapes and mounting positions:
- Downtube batteries sit low and central on the frame, which usually gives the best balance and a lower centre of gravity.
- Rear rack batteries mount over the back wheel, often used on step-through or folding frames where there's no room on the downtube.
- Triangle batteries fit within the main frame triangle, common on mountain-bike-style e-bikes and conversion builds.
When replacing a battery, the mounting style and frame fit matter as much as the electrical spec — a battery with the right voltage and Ah won't help if it doesn't physically fit your frame or connector.
Cell brands: does it matter?
Inside every pack are individual lithium cells, commonly from brands like Samsung, LG, Panasonic or EVE. Reputable branded cells tend to offer more consistent performance and a longer usable lifespan than unbranded cells, particularly for charge-cycle durability. It's worth checking which cells a battery uses, especially for a higher-mileage or daily-commute bike where longevity matters more than a small upfront saving.
Charging and looking after your battery
- Use the charger supplied or specified for your battery — mismatched chargers can affect performance and safety
- Avoid regularly running the battery down to empty; partial charges are generally kinder to lithium cells long-term
- Store at roughly 40–60% charge if the bike won't be used for an extended period, and avoid extreme heat or cold storage
- A battery with a key lock or removable design makes it easier to charge indoors separately from the bike, which is useful for security and for avoiding charging in direct sun or a cold garage
Before you buy: a quick checklist
- Confirm the voltage matches your motor/controller system exactly
- Compare batteries by Wh (V × Ah), not Ah alone, if voltages differ
- Check the physical mounting style fits your frame
- Look for reputable cell brands if long-term reliability matters to you
- Check whether a lock/key and charger are included
Next steps
Browse our full range of UK e-bike batteries, or if you're building or upgrading a bike from scratch, take a look at our electric bike conversion kits, which pair motors and batteries as matched systems.