This device has two uses: 

See also

I expect that new dongles are available before 3-2023 

Yamaha battery dongle PCB TS
Yamaha battery hack / Wireless battery Fuel Gauge / Watt meter


Please post your questions about the Yamaha dongle on this Endless Sphere discussion topic.

User manual

User manual

Hacking the Yamaha battery

As with other brands, the Yamaha PW series motor doesn't allow to use any 3e party battery. But with the use of the dongle described here, the Yamaha ebike will be hacked so that you can use any battery instead of the original expensive Yamaha battery.

At electric bicycles, only a battery of the own brand can be used, that is product tying and is prohibited, see my article HERE. If the same existed for cars, the 12V battery could not be replaced by any other battery, which is of course very undesirable. As with other brands, the Yamaha motor blocks also if another battery is used. But a Yamaha ebike can easily be hacked because Yamaha doesn't use any encrypted authentication. 

To develop a hack, GamerPaddy re-engineered the Yamaha mid-drive motor at the Pedelec-Forum. The battery dongle described here is based on the hack from GamerPaddy, but has several improvements such as the fuel gauge with the LTC2944.

Battery authentication, how does it work

As with all e-bike motor manufacturers, the motor blocks when another battery is detected than the same brand. Note that this is unallowed product tying, see my article Product tying.

The data line is a so-called open collector system that allows the battery to send a data to the motor. The 4.7kOhm pull-up resistor to 5V is located inside the motor. Both de motor and the Yamaha battery have an open collector output by which they send the data. After power on, the motor makes the data 5V for a few seconds. The motor is now waiting for a correct data signal from the battery. If no correct data is received after two seconds or so, the motor makes the data 0V and the system is turned off.

If something doesn't work you can check if the data is 5V for a few seconds after power on.

Fuel gauge with the LTC2944

The Yamaha battery has a fuel gauge built in and the battery capacity is sent to the display via a data cable. If a battery other than the Yamaha battery is used, the capacity should be measured externally. Therefore, the dongle also measures the battery capacity.

Characteristics of the Yamaha battery dongle

  1. You can use any battery on your Yamaha ebike instead of an expensive original Yamaha battery.
  2. The absolute maximum voltage is 50V, that corresponds to so-called 36V batteries.
  3. The battery capacity is measured very accurately with an LTC2944 fuel gauge IC, not just simple voltage measuring.
  4. Fuel gauge indication with 6 LEDs on the board
  5. To save power, the dongle turns off automatically when the Yamaha ebike is turned off.
  6. The battery capacity is stored in an EEPROM so that it is not lost when switched off.
  7. The data signal output has a short circuit protection.
  8. A NRF24L01 wireless module can be soldered for use as a battery monitor / fuel gauge / Wattmeter.

All Yamaha drive units X2 ST TE CE X2-45

Here are all Yamaha drive units as of April 2021.

All Yamaha motors drive units X2 ST TE CE X2-45
All Yamaha motors drive units X2 ST TE CE X2-45

Giant Syncdrive motor

The Syncdrive motor from Giant is just a Yamaha motor under a different name. However, it uses another communication system than Yamaha, namely the CAN-bus. This means that the dongle can’t be used here. But the good news is that the Giant Syncdrive doesn’t need a dongle at all and that you can simply replace the battery with any another battery with the same voltage.
Please contact me if you have a Giant Syncdrive motor where this doen't work.

Dongle installation

You must have technical insight and be able to use a multimeter, otherwise I can't help you if something doesn't work.
The dongle turns on only when the Yamaha motor is connected and turned on.

The first dongles don't yet have a protection case. You can electrically insulate the dongle with duct tape or heat shrink tubing. Make sure that the dongle is protected from water.

Yamaha battery dongle wiring

Attention: in case of wiring errors or reversed battery voltage, the dongle and the Yamaha system will immediately break. So double check the wiring with a multimeter before plugging in the battery.

Note that the charger cable can no longer be plugged into the charge input of the battery. Because the dongle contains the coulomb counter for measuring the battery capacity, the charging current must also flow through the dongle. It is best to use the anti spark XT90S for the charge connector.

Yamaha dongle connection
Yamaha 3rd party battery hacking dongle connections

User manual

To correctly display the battery capacity on the Yamaha display, a new dongle has to be set, see the user manual for the Yamaha battery dongle.

  • Set the specified battery capacity with menu 1
  • Fully charge the battery
  • Set a new charge cutoff voltage with menu 4

When the battery is fully charged, the fuel gauge will be automatically set to 100%. All leds will blink as long as the battery is 100% full. View the menu system for the other options.


  • Is it necessary to dismantle the motor?
    Not, the wiring is on the outside.
  • Which Yamaha motors are suitable for the battery hack?
    The dongle is till now just tested on the PW-X2 and the PW-SE motor, but it should work on all Yamaha mid-drive motors. If it unexpectedly doesn’t work on your motor, you will get the money back.
  • Which Yamaha motors are NOT suitable for the battery hack?
    Yamaha motors used on Giant ebikes.
  • Is it waterproof?
    The first versions will not yet be waterproofed, you have to take care of that yourself.

Connecting a second battery to a Yamaha battery

Instead of a battery hack, you can use the original (possibly worn out) Yamaha battery only because of the data signal and connect a new extra battery in parallel with it. I have described this in the article: Battery management system BMS.

Connecting an extra battery to a Yamaha battery
Connecting an extra battery to a Yamaha battery

Using the dongle for a 3rd party battery charger for a Yamaha battery

The Yamaha battery charger has a 4 pin connector and may use some protocol. I haven't had time to delve into this yet, so I don't know if the dongle can also be used for this.
If anyone knows more about this I'd love to hear it.

Example of other use

On my solarbike, the Maxun One, I want to use a Yamaha PW-X2 mid-drive motor. The problem is that the Yamaha battery is not suitable for my solar bike because:

  • The PV panels can charge the battery with a current as high as 8A. Normal Li-ion e-bike batteries can’t stand this high charge current. I need LiFePO4 battery cells.
  • The battery must allow simultaneously charging and discharging, this isn’t possible with the Yamaha battery.

LTC2944 ringing

In some rare situations, the combination of the low loss ceramic capacitors inside the Yamaha motor and the dongle may cause ringing. This leads to overvoltage transients, which may reset the fuel gauge chip LTC2944. If this is the case on your ebike, the following modifications will help:

  1. An electrolytic capacitor of 100uF 100V across the 36V supply voltage:

Capacitor 100uF 100V

  1. A resistance of 1 Ohm between the battery - and the gnd of the PCB:

Yamaha battery dongle v9 modification
Yamaha battery dongle v9 modification

The modification after applying heat shrink tubing:

Yamaha battery dongle v9 modification
Yamaha battery dongle v9 modification

Protected data output circuit

The Yamaha PW-SE data output circuit is not protected against short circuit to the battery +, the transistor TR320 will be blown up then. That's why I reverse engineered the data output circuit. The dongle has a protected data output that is protected against short circuits.

Yamaha PW SE data output circuit

Blown up transistor TR320 (EMG9) PW-SE Yamaha
Blown up transistor TR320 (EMG9) PW-SE Yamaha

Dongle during development 

Yamaha PW X2 serial data
Yamaha PW X2 serial data

Yamaha battery dongle development
Yamaha battery dongle development

Pedelec forum


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