External battery for Xiaomi M365/PRO/1S

It's no secret that many owners of Xiaomi M365 and PRO would like to increase the range and speed of their scooter.

This can be achieved in two ways: the first one is to replace the battery to a more capacious and high-voltage one, or the second way is to keep the original battery, installing an additional external battery.

In the following two videos I will show you how to install an external battery to the scooter, and this battery can be easily connected or disconnected at any moment, without voltages equalizing. We can even use a higher voltage external battery, like 48V.

The first video is long and full of theory:

The second video is focused on installation process and testing, so it is shorter and simpler:

As usual, I made a short text version for people who prefer reading rather than watch the video. But this text contains only 30% of information, so I highly recommend to watch the videos.

Let's get started!

The following 3 parts are required to equip the scooter with an extra battery:

1. 1) battery
2. 
3. 2) mounted bag
4. 
   
5. 3) adapter to match external and internal batteries - "Rita"
6. 
   
7. Battery

Of course, this part is the most important. "Bigger" battery - more energy and more range. "Bigger" means 2 things:

1. More capacity
2. Higher voltage

Increasing capacity, you improve range. Raising voltage, you improve maximum speed.

Obviously, you want everything at once. Therefore, usually people install a battery with both increased capacity and raised voltage.

But you must be careful, because maximum battery voltage it is limited by the scooter controller. The original battery voltage is 36V, or, in other words, 10s. 10s means that the battery contains 10 serially connected parallels, each of 3,6V.

The scooter controller withstands voltage up to 48V, so the battery configuration may be easily increased up to 13s, giving 30% more speed.

Regarding the battery capacity - you can make it of any value you want, if only it fits in a bag. My bag holds up to 50 18650 cells, so it’s possible to make a 10s5p battery, which will only give a range increase, or 12s4p, which will provide an increase in both range and speed.

You ask me: why do I consider 10s5p battery if 12s4p is better? Well, 12s has one disadvantage - it can not be charged with original charger, and you need to buy a higher-voltage one, or modify the original charger.

Finally, in my opinion, 12s4p battery is the best choice for external battery.

Mounted bag

There are still no factory-made bags with a rigid mount on the scooter frame. Therefore, the main idea is to get any cheap standard bag, and equip it with a self-made plastic 3d-printed mount.

Here is the mounted bag I designed:

You can see that the mount matches the shape of the scooter frame, so a single clip is enough for a secure fit. Thus, my bag is easy to install and cheap.

Adapter to match external and internal batteries

We need to use a special adapter because of fundamental problem - the voltage of a battery depends on it's charge level:

And if we connect these batteries in parallel, the current starts to flow from more charged one to less charged one, like water in communicating vessels:

Finally, the voltages will be self-aligned:

But the current between the batteries can reach significant values during the charge flow process, and charge current like this are not allowed for batteries:

Therefore, we must block the current between the batteries, and the first idea is to use 2 diodes for this purpose:

But this simple solution is not acceptable to the electric scooter, because it's controller not only drain current from the batteries, but also recovery energy back when the brake is pushed. Diodes block the energy recovery current, therefore voltage at the controller instantly rises up, and the controller burns out.

So, we need a smarter circuit that could distinguish energy recovery current and current between batteries. This circuit must analyze controller and batteries voltages, and decide which current should be passed, and which - blocked. And this circuit also must connect to controller's data line to provide information about additional battery state:

I developed this smart circuit, here it is:

I named it "Rita". Why? Well, the answer can be found in the first video at the beginning of this article =)

Ok, finally, we reviewed all the devices needed to install an extra battery.

Let's pass to the mount process.

The first step is to secure the bag:

After the bag is mounted, you can still put your feet on the scooter and fold it:

Then, let's install Rita inside the scooter and plug all wires:

And finally plug in the external battery:

All done! The additional battery is successfully installed!

Let's pass to the range and maximum speed tests.

I use a 12s4p external battery, based on LG M26 cells, so my battery is 10400mAh of capacity and 44.4V of voltage.

I spent the whole day riding the scooter, to compare the single internal battery and internal battery coupled with additional external one.

Here are results I got:

Seems not bad!

And now I am really happy with this external battery. Before I installed it, I had to constantly worry if I had enough battery charge, plan a route on the map and think about where to recharge on the way. With the external battery I just ride the whole day where I want, and never worry about charge level.

So, I highly recommend everyone to install an additional battery for Xiaomi M365, PRO and 1S electric scooters. This is a whole new level in usability.

Here are links to the equipment I used:

1. "Rita" adapter - https://m365.embedden.com/rita_adapter
2. Mounted bag - https://m365.embedden.com/mounted_bag
3. External battery 10s4p 13800mAh - https://m365.embedden.com/36v_13800mah_battery
4. External battery 12s3p 10350mAh - https://m365.embedden.com/44_4v_10350mah_battery
5. 12s charger - https://m365.embedden.com/12s_charger
6. Complete all-in-one pack to boost the range (10s battery + Rita + bag) - https://m365.embedden.com/range_boost_kit
7. Complete all-in-one pack to boost the range and speed (12s battery + Rita + bag + 12s charger) - https://m365.embedden.com/range_speed_boost_kit

I also invite you to join my telegram group related to Xiaomi M365, PRO and 1S electric scooters:

https://t.me/m365_custom_electronics_en

Russian edition of this post: https://m365.embedden.com/article_xiaomi_m365_pro_external_battery_ru

Thanks for your attention!