There is a phenomenon known as voltage sag and it happens to all batteries in certain situations. If there his a high demand for power, for example: If you are going up a hill or are in  pedal assist 5 using 95% power or throttle, and or riding into the wind, this will consume a lot of power. The voltage read out of the battery while this is happening is going to read lower than it actually is and will read low for some time after. If you stop at a red light, you might see it come back up a little in just a minute.

The amount of voltage sag, or how much lower it will read depends on how much power was being drawn from the battery and sent to the motor. Essentially, we cannot read the voltage accurately to determine how many amp hours are remaining while there is a large demand for power from the battery. Once this high power draw stops, the voltage will adjust slightly and come back up. For example if you stop riding for a while or even if using 800W of power, and then switch to pedal assist 1 and am only using 250w of power, the battery may start to read more accurately. Once you come to a stop, and let the bike sit, in 1-10 minutes you may see the voltage rise to its current accurate voltage. 

When the voltage sags like this, if it sags too low (below the required voltage for the controller and motor to operate), the controller will stop sending power to the motor until the voltage returns to normal. On a larger battery, you are less likely to see this, on a medium or small batter, as you run the battery percentage down, you are more likely to see this. So if this happens while you are riding, and your battery is low, it is probably best to lower your PAS to level 1 and continue your ride in that fashion. If the bike powers down because the battery is too low even in PAS 1, it is best to not turn the bike on. Return home and charge it as soon as possible.

Here is a 3rd party take on it from the EBR Forums: https://electricbike.com/forum/forum/knowledge-base/batteries-aa/48140-voltage-sag-explained



RANGE TEST:

If you understand voltage sag, but are still concerned about your batteries performance, it may be best to test your battery range, use the trip meter on the bike and review the following checklist:

  • Charge the bike to 100% (the charger's LED should turn from red to green), it is best to cycle (drain and recharge) the battery 3-5x to reach maximum capacity.
  • Ride in PAS 1 or 2 (verify % setting in display)
  • Pedal hard or moderately during your ride.
  • Monitor how many Watts (W) are going to your motor (Press the middle button 3x)
  • Tires are at max psi (listed on the side of the tire) - soft or knobby tires can be a huge drag
  • Front  and rear wheel spins forward freely and true. It should continue to spin for quite a while and not slow down prematurely
  • Brakes are properly adjusted and not rubbing
  • No accessories, racks, fenders, etc are rubbing against the tires.

Other things that can impact range greatly that we will avoid for the purpose of the range test:

  • Riding into the wind
  • Riding up hills
  • Riding in a high PAS level
  • Weight of rider, accessories, and cargo
  • Using Throttle a lot
  • Accelerating from a stop. The more you stop and start, the more power is used
  • Extreme temperatures
  • Rough terrain
  • Knobby tires


Did you hit or exceed the expected range? If not, please let us know. This is a good way to confirm if what you experienced, was indeed just voltage sag, and that your battery is giving you the expected range for your model.