How I added a battery 🔋 to my Scooter 🛴 E-Bike 🚴‍♂️

I ordered 4 batteries from China to attach them to my e-bike (Fiido D4S). I want to put them in parallel to get more range for longer trips or use them separate and change them when one is empty. I also want to put batteries in series to have a higher voltage than 36V, i.e. more speed. But that is not so easy. (In the meantime I bought a separate 48V battery because putting in series is kind of difficult.) Please read on to see how I did it! (Es gibt diesen Artikel auch auf deutsch 🇩🇪!)

My batteries

These are the batteries:

12V is on top, below is 2x 36V

In the meantime I bought a 48V battery:

48V battery

  1. Liitokala 36V 12Ah (to extend the range if added in parallel to the bike battery)
  2. another Liitokala 36V 12Ah (for my girlfriend if she ever buys another e-bike to use instead of her scooter)
  3. LiitoKala 12v 12Ah (to add in series, i.e. to test 48V capabilities) -> not recommended
  4. I bought a separate 48V 10Ah battery (because putting the 12V and the 36V in series would be too complicated) – Note: 48V can destroy your motor if you have just a 36V/250W one

36V 12Ah Battery @ aliexpress 48V 10Ah Battery

LiitoKala vs. Small Den

In the future I will only buy batteries from Small Den, they give a more honest capacity, have factory direct sales, customer customization and good reviews.

And they have 21700 which I have not seen yet:

36V 13.6A (10s4p 18650)  –> same size as D4S battery!!! 36V 10A (10s3p 18650) –> incl. fuse!!! 36V 15A (18650) 48V 10A (13s3p 18650) 48V 9.6A (13s2p 21700) –>21700 48V 15A (13s5p 18650) 48V 20A (13S6p 18650)

Bag

You can put the battery in this bag for example on the seatpost (or the handlebar of the scooter or below the handlebar), or you put it on the luggage rack:

usually you would hang the bag from the handlebar on a scooter…
…but this is the place you would typical mount it
(check out thingiverse.com for 3d printable adapters)

Both the 36V and the 48V battery fit into the 3l bag, but it flops around a little bit when driving:

fitting the 36V battery into the 3l bag is easy (actually fits into the back department)
one downside of the 3l bag is that I cannot put the seat down enough for my gf
(no problem with the 2l bag or you put it on the rear rack)

Only the 36V fits into the 2l bag and it is a snug fit… which may be a good things because it does not move at all while driving:

the 36V battery is a snug fit in the 2l bag

As you can see I bought the “old” version with Velcros (the new version has a click-in system):

from left to right: 2l bag, 3l bag, 48V battery, 36V battery

I think the “old” version is more secure when fixing with the velcros to the bike seat:

the velcros take more time to open, but you can take the whole seatpost with you
as a theft protection
old version

This is the “new” version, if I would carry something more lightweight I would prefer it:

“new” version,
I suppose the plastic mount cannot hold a heavy battery
(but you could fix it using extra cable ties)

36V 12Ah @ aliexpress 12V 12Ah 48V 10Ah Battery Bag @ Amazon (old version) Bag @ aliexpress (old version) Bag @ Amazon (new version) Bag @ aliexpress (new version)

Connecting external batteries (Version 1 of my update)

To add the batteries I could splice an XT60 cable onto the E-Bike battery cable and add it in parallel like in this video:

But I want to be able to use just an external battery as well (or 2 external batteries in series). So I also followed the instructions in this video:

Because when adding a battery in parallel it has to be the same voltage (and maybe I don’t always want to drive around with 2 batteries…). I.e. I would have to charge both batteries at the same time (and if I have used only one charge them seperatly). And – very important – I also want to use an 48V battery in the future. I came up with this design:

I created these two XT60 cable contraptions:

XT60 male and female… positive is where the square is, negative where the triangle is (don’t solder it wrong!)
Note: You can buy the original battery shell “thingy” from Fiido if you don’t want to “destroy” it (so you can always “switch back” to normal…)

The cable to the left is connected to the controller and the cable to the right is connected to the internal battery. Connecting both cables together uses the internal battery:

using the internal battery

Using another XT60 Y-Cable I could connect an external battery in parallel (has to be the same voltage!!!) for more range. (Usually 2 batteries in parallel last longer than 2 separate ones!)

Or I disconnect the internal battery if I want to use the external battery only (might need to add a switch because unplugging the XT60 is not always so smooth):

using just the external battery

Parallel cables can be bought from Aliexpress or I will make my own:

parallel cables

I also added two more cables so I can power other devices (bike lights, alarms, GPS, etc.). I should have used thinner cables but I had to work with what I have. I used a WAGO terminal so I can easily add devices (someday I will put real connectors):

WAGO terminal for 2 additional devices

You can buy a similar cable on Aliexpress and save yourself a lot of trouble:

I also added an automotive fuse. This is completely optional. But because with thinner cables and devices with less wattage, they could burn in case of a short circuit.

automotive fuse

I soldered it but I really should have used crimps (or bought an inline fuse). But the fuse was only 1 euro, so who I am to complain?

soldered the fuse to the circuit (should have used an inline mini fuse which requires less space)

36V 12Ah Battery @ aliexpress 48V 10Ah Battery Wire Stripper (I recommend not to use automatic ones like I used because it will damage the wire) Heat Shrink Tubing Insulation Tape Wirecutter Voltmeter Hot Glue Gun Helping Hands Tabletop Loupe with LED Soldering Iron Fuse 14 AWG Silicone Wire 22 AWG Wire WAGO terminals XT60 connectors

Black Box

I plan to put the fuse and all small devices like GPS, bike alarm and Samsung SmartTag Plus (it is similar to Apple AirTag) in a small 3d printed box (“black box”) in the triangle above the bike stand (if you don’t have a 3d printer you could buy a small waterproof bag instead or put everything into the external battery bag):

First Prototype
the small rings are to connect a lid (this is in Cura)

I used tree supports to print it:

This idea is heavily inspired by the design that Jonas Krug showed in the Fiido D4S facebook group.

I use the screw of the bike stand
here I put the bike alarm for testing (had to use bubble wrap because it is loud… which is good I think)
Bike alarm in action

The battery will go into a bag attached to the seatpost.

I also think this is genius:

this even protects the controller exit on the bottom of the frame… I used it to temporarily house the XT60 connection

Joe Fallkon basically used a neoprene smartphone armband to put a wattage meter inside. This is even waterproof and with a transparent window (where I can check my connection)!

Well I still plan to put the cables into the 3d printed box, but I still need to design a lid and that’s where I will put it!

My 3d Printer (Artillery Genius) @ banggood.com Artillery Sidewinder @ banggood.com (bigger but I did not have space)

Version 2

Here are the main ideas for version 2 of my external battery update:

  • put a switch so I can select internal or external battery (and don’t have to unplug XT60 cables which is sometimes difficult)
  • put inline fuses for the internal and external batteries (>20A)
  • make a hole in the lid of the 3d printed box for XT60 (to quickly connect external battery) and switch (waterproof if possible)
printing the lid (with an opening for the switch)

This is the design of the switch:

all cables
inline fuse
splitter cable to connect alarm and GPS
putting everything together (I used threaded inserts for the screws to join the two parts)
already installed (in off position)
I can use the remote to activate the alarm and put the external battery into the pannier (I plan to use a bag on the seatpost but it did not arrive yet)

What I learned from Version 2

  1. I used spade connectors to connect the XT60 connectors to the switch. I am not completely happy with this, I think soldering can support more Amps. (I soldered the first switch and melted it inside…)
  2. I attached the alarm and the GPS to the internal battery, so it is always on (even if the switch is set to off). I am not completely happy with this solution, but I was afraid the thieve could find the “killswitch” and turn the alarm off…
Maybe I should have bought an On-On switch instead, or this On-Off-On switch with soldering pins (DPDT, 6 soldering pins, On-Off-On, Latching, with waterproof cover)

It is still possible to turn the alarm off by folding the bike, but the GPS has a small battery and will stay on for some time!

  1. The switch is not glowing, this is because I bought the 220V version by mistake. Next time I would probably just buy the black version (without LED).
  2. I bought a “mini” (inline) fuses to save space. The disadvantage of this is that you need a plier to remove it. (“Standard” sized fuses can be changed just using your fingers.) I used my 3d printer to print it:
fuse puller

DPDT Switch 30A/250V (Aliexpress) Retro Switch (DPDT, 6 soldering pins, On-Off-On, Latching, with waterproof cover) 3d printer (Banggood) Inline Fuse (Amazon) Spade Connectors XT60 connectors 14 AWG silicone wire 22 AWG silicone wire Crimping Tool for Spade Connectors JST SM connectors Crimping Tool for SM connectors Heat Shrink Tubing

Recommended camera equipment for photo, video & travelling (AMAZON):
Sony a6600 Sony a6400 (cheaper) Sony a6100 (Budget-Option for 4K) Sigma 16mm 1.4 Sony 35mm 1.8 Samyang 12mm 2.0 Feelworld Master MA7 Smaller monitor Rode VideoMicro Rode Wiress Go II Mini Tripod Travel Tripod Small LED-Light Light #1 (powerful) Light #2 (Bi-Color) Softbox for this light Light tent/box DJI Osmo Action GoPro 9 GoPro MAX Invisible Selfie Stick Mavic Mini 2 drone Mavic Air 2
for photo and video:
Fuji XT-4 Fuji Telezoom Entry level camera (Canon)

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