I've marked a few possible places for additional battery mount.

What do you think is the most reliable place to mount battery in terms of ergonomics of the bike? Also, how to ensure the parts are having waterproof connection?

Model is OIO City Bike

Additional specs:

 Wheels diameter: 26 inches

 Motor: 350 Watt, brushless, maintenance-free

 Speed: 35 km / h

 Weight: 21 kg

 Load: 120 kg

 LCD Display (KBY-DISP KD21C): Indication of battery charge status, support level, speed

 Number of gears: 21

 Brakes: Disc

 Frame: Aluminum

 Battery: 36V 10.4Ah Li-ION

bike scheme

  • I do not understand your question. Did you already solve the electrical engineering part? Do you want to carry there just as a spare or is it supposed to be connected to the motor? You can carry a spare anywhere you want. Is the main battery user-replaceable at all? Commented Oct 15, 2020 at 8:30
  • Please clarify this: "However, it's unclear for me what would be the best solution to change between them since original battery is integrated into the downtube." If you want us to tell how you swap batteries in your bike, we cannot know that, we do not have your bike. Commented Oct 15, 2020 at 8:31
  • There may be a trigger based activation, such as after main battery is certain %, it disconnected and spare battery is turning on, this option requres microcontoller. More simple is manual switch.
    – Boikameri
    Commented Oct 15, 2020 at 8:36
  • 2
    And also remember that you have an infinite secondary battery, in that its a pedal powered bicycle. If the main battery runs flat, just pedal like normal. Its not a motorbike - its an electric assisted bicycle.
    – Criggie
    Commented Oct 15, 2020 at 10:21
  • 1
    I’m voting to close this question because its about the electronics to switch between battery packs and not about bicycles
    – Andy P
    Commented Oct 15, 2020 at 13:01

1 Answer 1


I'm going to assume that the question is:
Where is the best place to put an extra battery that will:
- Optimize weight distribution
- Be out of the way / not interfere with general bike operation

All three areas you have identified as options are used on touring bikes to store luggage and are reasonably interference free.
The two options inside the front triangle make sense because those locations tend to distribute the weight of the battery to both wheels.
Having an extra battery on a rack over the rear wheel will put all of the weight on the rear wheel only and it will take up space that could be used to carry other things.

I recommend mocking up something inexpensive that mimics the size and weight of the spare battery and trying it in different places. You may need to make a couple of mock ups but experimentation is the best way to learn.
When you have found the best location, size, shape and how to attach it for your use case you can spend money on actual hardware and know what you need.

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