Bike Battery Bad? The Load Test


Another year, another bike. This one is much lighter than the last one, but has terrible range. Let’s dig in.

So I have had 3 ebikes that I have commuted in the winter from home to work. Same route, same weather, etc. The Voltbike Yukon (bike #2) was 750W, rear hub, 48V @ 17.5AH. I would charge it about every 3rd day in winter.

The Biktrix Jugernaut Ultra Beast (bike #3) was 1500W mid drive, 2 x 48V @ 15AH. It was also a super heavy bike. I would charge it about every 3rd day in winter.

Both of these two had 26×4.8 snow tires with carbide studs.

The current bike (Biktrix Duo) has 1000W mid drive, 1x 52V @ 17.5AH, mid drive. It needs to be charged daily or it runs out of juice.

Now, its reasonable to assume I drive all 3 the same fashion. Same amount of assist, same path, same weather, same distance. The current one is by far the lightest, and has the least resistance tires. I would expect it to have the best range (even tho the juggernaut had more watt-hours).

So, time to bring some science. And by science I mean jury-rigged hackery. Now, I don’t have a big enough load tester to discharge @ 1C. The battery is ~1kWh, so 1C would be a 1000W load. Instead I have acquired a 250W load. So, we will discharge at C/5 (20%). This should be very easy on it.

You can see in the photo above the beautiful setup:

  • tailgate of truck
  • old phone set to timelapse
  • digital load
  • 2 keys to a previous bike battery shoved into the receptacle

A 52V battery has a peak voltage of 58.8V, is at 50% capacity at 52V, and is dead somewhere around 46V. Place your bets.

Update, below the results.


2 Responses to “Bike Battery Bad? The Load Test”

  1. Your math seems a bit off. Back of napkin: approx 200W for 4h should be around 800W*h
    Even ignoring the tail, after 3h of over 200W should be well over 600W*h

    • Don’t think so, the voltage drops a lot. Its not a constant 200W, its a constant 4A.

      — edit, suddenly a wild math error. Turns out there are 24 hours in a day, not 14! Updated chart.

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