There is a phenomenon known as voltage sag and it happens to all batteries if there his a high demand for power.


Examples

  • If you are going up a hill or are in pedal assist 5 using 95% power or throttle
  • Riding into the wind which also consumes 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 is 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. Even if you continue your ride, but switch from using PAS 5 (600-800W) of power to PAS 1 (using only 250W) the voltage will come back up given a little time. 

If you come to a stop, and let the bike sit, in 1-10 minutes the voltage will be more accurate. If the voltage 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 unless the battery is low. On a medium or smaller battery, it may will be more common if you often use the full range of your battery and use high PAS levels. If this happens while riding, and your battery is low, it is best to use PAS 1 and continue your ride. 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 Tests


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% (Verified by the charger's LED changing from RED to GREEN).
  • To reach maximum capacity, drain the battery low and recharge to 100% 3-5 times.
  • Ride in PAS 1 (verify % setting in display, is yours set to 10%, 20%, etc?)
  • Pedal hard or moderately during your ride.
  • Monitor how many Watts (W) are going to your motor if possible (Varies by model. LMT'd/700 Series W is displayed. 500 Series/Core-5/Cafe Cruiser: Press 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, or fenders are rubbing against the tires.


Factors to avoid during a range test that can impact range

  • 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.