How to choose a battery

How to choose a battery

Just about all new eBike batteries are Lithium Ion – if you see anything else for sale – run a mile!  Whatever you end up buying, the large single battery will contain lots of small ‘cells’ that look a bit like those batteries you put in your torch. The only thing we recommend  you check  is who makes the cells? The actual pack could have been made by anyone – but you want to be sure your cells are a known good brand if you are sure they are going to last. We recommend Samsung, LG or Panasonic. If in doubt, check with the company that makes the battery pack. If they don’t state who made the cells, then there is probably a good reason!

You do however have three key choices. What battery voltage, where to mount the battery, and how big should the capacity be.

Battery Voltage

Most motors will specify the voltage they need, so this choice is probably fairly easy – simply buy what the motor demands.

In the past few years, voltages tend to be 36V, 48V or 52V. In general, 36V tends to be used on smaller 250W motors, and 48V on 500W or greater motors. However, in recent years, 52V batteries which many 500W plus motors will also cope with, have been coming out. These offer greater range and speed, but if the motor and controller are not suitable for the higher voltage, you risk damage. They also tend to be more expensive..

Battery Capacity

This depends on two factors – how far do you want to travel, and how big is your motor.

It’s easy to work out how long your battery will power you along. Every battery has a voltage and the number of amps it will put out for 1 hour (AH). If you multiply these together, it tells you how many Watts your battery will put out in total. For example, if your voltage is 48V, and your battery is rated at 14AH, then multiply both numbers together to give you the number of Watts – in this example, 48 x 14 = 672 Watts.

Assuming that you will always leave 20% of your battery in reserve, this gives you 537Watts. If you motor is 500W, this would power you at full speed for just over an hour. If it was 750W motor, you will get 40 minutes. However, you don’t ride at 100% power all of the time. If you ride using just a third of the power, the 500W motor will last for 3 hours, and the 750W will last for 2 hours.

If all of this is too complicated, just remember that bigger batteries cost more, so consider how far you want to travel vs how big your budget is.

Mounting Options

Rear Rack Mounted

  • Works best for a small, lightweight battery
  • Keeps the battery out of the way and frees up space within your frame for a drink bottle
  • As it is mounted at the back of the bike, it isn’t best for off road use as the handling of the bike can be impacted

Frame / Downtube Mounted

  • Most common type of mounting for a self build ebike
  • Attaches to bottle mount so very easy to fit
  • Weight is in centre of bike and can be low down for good balance
  • May need an additional rivnut as the bottle mount may not be strong enough
  • Can be vulnerable to knocks

Triangular in frame mounted

  • Can fit suspension bikes that you can’t fit a frame/downtube battery on to.
  • Huge capacity so often much greater range than other battery types
  • Mid frame mount so good weight distribution
  • Quite large and heavy

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