Fiido 2 Electric Folding Bike - External Battery EBike

The internal battery (stored inside the frame) failed and was replaced by a second internal battery which also failed. So I wanted a better quality battery which I could remove to charge, and would be easy to replace.

The final solution is shown in the photo above - there is no internal battery at all.

This instructable is not a step-by-step walk-through, just a series of photos to give inspiration for others, and to prove that and external battery can be fitted to this small, folding bike.

The battery, charger and mounting plate bundle cost £150 (April 2026) from what I hope is a good UK supplier (time will tell about the longevity of the cells). It theoretically almost doubled the energy storage from 7.8Ah at 36V to 13Ah at 36V.

I purchased the battery from Yose Power UK. It came quickly to my address in the UK, was packaged well and was complete. I have only just started using it, so don't know how good it will be into the future. However, the indicated energy reserve had not gone down much over the short journeys I have done, and (unlike before) when I accelerate hard, the Fiido energy indicator on the handlebars stays firmly on 'Full' rather than dipping down and recovering (I think this indicates that the battery voltage of the new battery stays close to 36V, even when supplying maximum current, whereas the voltage of the original inbuilt batteries fell considerably when maximum current was demanded).

I had to purchased 1m of red and black 12 gauge battery wire.

These photos show the final result. I was going to 3D print a mount (there is a good YouTube video from a guy who has mounted a similar battery to his Fiido D2, and that looked to be a very good solution) but when I designed a suitable 3D mount, each half was going to take 1½ days to print, so I made the mount from what I had 'in stock'!

The only critical dimension was provided by the square steel tube, on which everything is mounted. This tube had to be 25mm x 25mm to raise the battery up from the main bike tube, so that I could accommodate the full length of the battery without fouling the hinge mechanism (it overhangs the hinge a bit).

I drilled a 12mm hole in the top of the bike's main tube, so I could feed the wires through to the internal hinge connector (as is used in the original Fiido design).

You can still fold the bike, with or without the battery inserted into its mount. The bike always was a handful to deal with when it was folded due to its weight, if I leave the battery mounted, the bike is even heavier than the original, however removing the battery (with the supplied key) makes it a little lighter, so slightly easier to manhandle.

I did 3d print some tiny covers for the rather ugly tightening screws for the mounting straps.