E-bike battery. How to choose one?

Whether you are buying an electrification kit or electric bicycle, it’s quite important to understand what battery to choose. Batteries are one of the most expensive components in e-bikes. They also can be made of different materials. What technical characteristics are suitable for me? How much will I be able to drive on a single charge? Why is Li-ION battery better than NiMH battery? These and other issues are covered in this article. Ebike rack battery

At the end of this article, you can find explanations of terminology used here. So if you think you don’t understand something, e.g. amp-hours, check that first.

First, let’s sum up what matters to e-bike owners when they choose battery for their e-bike. Usually, it is traveling distance, weight, lifespan, and price. We will explain briefly each of these matters one by one.

Traveling distance

The price of a battery almost linearly depends on the maximum traveling distance. This means the battery with 80 km range will cost two times more than the one with 40 km range. Hence, pick up the battery with needed energy capacity so that you won’t overpay for extra range.

If you want to know how far you can go on any battery, use following formula: Normally, in pedelecs (250W e-bikes) engine requires 8 Wh/km. It may vary depending on terrain, drivers’ weight, speed and pedaling. If you have 36V 8.8Ah battery, you will be able to ride approximately 40km on a single charge.

Some manufacturers may claim higher ranges, but they usually consider perfect conditions like lower driver’s weight, flat terrain, an absence of headwind, little engine support level, etc. 8Wh/km is somewhat an average value for normal usage that gives a general understanding.

If you have a 36V hub motor, then you should have a battery of same voltage, 36V in this case. Battery's and motor's voltages should match. Otherwise, you can damage controller and motor. Remember this when choosing battery for your e-bike.

Weight and size

Even if two batteries look identical, they might have different cells inside, hence possess different features. Lead-acid (PbA), Nickel-metal Hydride (NiMH) and Lithium have been commonly used chemistries in e-bike batteries. And one of the differences between them is weight.

  • Li-ION is lightest (~120 Wh/kg)
  • LiFePO4 is 1,5 times heavier (~80 Wh/kg)
  • NiMH is 2 times heavier (~65 Wh/kg)
  • Lead-acid is 4 times heavier (~30 Wh/kg)

Not only Li-ION battery is the lightest, but it’s also the most compact battery when it comes to the sizes. What does it mean in practice? Well, you can drive 40 km on 3 kg Li-ION battery or 12kg Lead-acid battery. High energy density is one of the reasons why Li-ION are nowadays most popular battery chemistries not only in e-bikes but also in other electric vehicles (e.g. Tesla cars).

Lifespan

A number of lifecycles mean how many times you can fully charge and discharge the battery before it will start losing its capacity. And different battery chemistries have a different lifespan.

  • Lead-acid: 250 lifecycles
  • Li-ION: 750 lifecycles
  • NiMH: 1000 lifecycles
  • LiFePO4: 1500 lifecycles

If you commute once a week, maybe Lead-acid’s 250 lifecycles will be enough for you. Though you still need to remember how heavy those batteries are. On the other hand, if you use your e-bike quite often, think of batteries that have a bigger lifespan.

Price

We are not listing here the prices, because they differ for manufacturers, quality of cells used and battery characteristics. For example, Li-ION battery may have the same price as LiFePO4 but first will have Panasonic cells inside and another just generics cells. But we can give you a general overview.

LiFePO4 is the most long-living battery, but at the same time most expensive. Li-ION is the most lightweight and usually cost ¾ of LiFePO4. The cheapest is, of course, Lead-acid, but nowadays nobody is using them that much due to its heavy weight and short lifespan.

As been stated before, price greatly depends on battery’s distance range defined by energy capacity. So, pick up the one that suits your needs.

Conclusions

To sum up, when choosing battery for your e-bike always consider its technical specifications, chemistry type and, of course, price.

Firstly, evaluate your commuting route, to know how much of range you need during the day. Then assess technical parameters like Voltage and Amp-Hours of your “perfect” battery. Secondly, choose suitable chemistry: Li-ION is for people who are looking for lightweight battery; when LiFePO4 is for the ones who plan to commute very often for years.

If you are installing electrification kit on your bicycle, usually you have two options: rack and frame battery. Choose wisely, always keep in mind weight balance. If you have a front-wheel motor, it’s better to install rack battery. In case you have a mid-drive or rear-wheel motor, you might think of frame battery.

Lastly, check if the final price suits you.

Battery Basics and Terminology

  • Voltage (V):
    • Typical e-bikes are designed to run on 24, 36, or 48 Volts. Higher voltage gives higher maximum speed. Important to remember that voltage of the battery should match motor’s voltage. Otherwise, you can damage your e-bike kit.
  • Amp-Hours (Ah):
    • Measures capacity of the battery. If a battery can deliver 1 amp for 1 hour, its capacity is 1 Ah. Most e-bike batteries have 8 to 12 amp-hours capacity. If the engine uses 8 Ah, 12 Ah battery will perform for 1,5 hours.
  • Watt Hours (Wh):
    • Measures “energy capacity” of the battery. Equals voltage multiplied by amp-hours. Defines the maximum distance you can ride. In general, the weight and cost are almost linearly related to its watt hours: twice the watt hours would mean twice weight and the cost. So 24V 8Ah and 48V 4Ah batteries will both provide 192 watt-hours and will cost, weight and provide almost same performance.
  • Energy Density (Wh/kg):
    • Shows how heavy a battery should be to achieve a certain distance range.
  • Lifecycles:
    • If you fully discharge the battery and then charge it again, it is called one charge cycle. All batteries have limited life and will gradually lose their capacity to hold a charge.