How to repair a DJI Mavic Air PB1 Battery with BQ40Z307
Published On: July 14, 2023
Battery Repair PB1 – 2375 Amp 11.4v battery for Mavic Air
Before I go into the steps taken to repair the PB1 battery I would like to give a short summary of my knowledge and experience coming into this repair.
I received a certification to work on DJI drones about 2 years prior to this repair. One thing that I have found, there are a lot of issues with the batteries discharging beyond the point where the charger can recognize and charge the battery. I have no prior knowledge or experience with troubleshooting or repairing batteries before this repair, though I do have a good understanding and experience with electronics.
I was searching for a pinout to this PB1 battery trying to determine if there was any voltage present when I found the site for the NLBA1 laptop battery analyzer. As I searched the site I learned that unlike a simple lead acid battery where there are cells and a voltage present, in the DJI batteries there is a circuit board and chips that determine the state of the battery. Once I learned that it was possible to clear the errors and restore the batteries, I ordered the NLBA1 and started my battery repair journey.
Troubleshooting the PB1
When the customer dropped off the drone they said it just needed a sensor calibration. When I tried to power it on I found that the battery was completely dead and the LEDs would not light up at all when the power button on the battery was pressed.
I found a pinout on the forum and connected the NLBA1 to the battery.
I tried to get a reading and was not able to read the battery data in the NLBA1 PC software.
I searched the forum and learned that when a battery is completely dead you must apply 12v to wake up the battery. So, I applied 12V to the battery with some jumpers and a DC power supply and then was able to get a reading on the battery. Later I learned that you can apply the 12V to wake up the battery through the NLBA1 software under the Apply Output Voltage, using the allow custom voltage and Power On button.
Now I was able to get a reading on the battery. I thought that Cell 3 was really low and Cell 4 was faulty. I asked a series of questions on the forum and learned that this battery only has 3 cells and because it only had 15 charge cycles, it was highly probable that the battery could be reset.
Below is a screen capture of the NLBA software. Note in the bottom left how the Battery Status is Locked, the Cell Balance is Bad Balance and the Max Imbalance is 1700mv between Cells 1 and 3.
I learned that the voltage imbalance between the Cells was causing the fault code that is shutting down the battery. In order to clear the fault code we must first balance the Cells, otherwise it will just keep generating the same fault code.
Balancing The Cells
In order to Balance the Cells, I had to open the battery housing. The PB1 has some small clips and a light glue that holds it together. I don’t have any pictures of the disassembly, but I was able to take a very small flathead screwdriver starting at the top by the connector, gently pushing in and separating the housing. Working my way down both sides I was able to separate the housing without much visible damage to the plastic housing.
Once open, I was not able to find any test or connection points on the board. Using a multimeter, I was able to find the positive and negative connections to the Cells and determine which Cell was bad.
Now I knew which Cell was bad and the voltage difference of that Cell. Cell three was bad at 1.74v. To balance that Cell I used a DC Power Supply set to 3.5v and 0.5Amp. I did not want to solder to the terminals, so I just held the leads to the battery. It took about five minutes for the Cell to charge. Note, on my Power Supply it gives a voltage reading, much like a meter mode on some power supplies. I was able to watch the voltage rise as the battery Cell was charging. This is how I knew when it reached 3.5V.
Picture holding leads and charging the battery.
Once the Cell was charged, I took another reading in the NLBA Software.
Now the readings showed that there was a much better value but still a difference of 62mV between Cells 1 and 2.
So, I balanced all three Cells this time. After balancing again I obtained a manageable value that shows balanced.
Though not ideal the voltage difference between Cells is now only 17mV between Cells 1 and 3. Now that the Cells are balanced within tolerance we can clear the fault code.
Clearing The Fault Code
Now that the Cells were balanced, I could go in and clear the fault code.
Because I have purchased the DJI reset license for the NLBA software, I have access to the reset tab in the NLBA Software.
With everything still connected from reading the battery data, I clicked on the Reset Tab.
Next, I clicked on New Reset, then Read SBS and clicked Next. Then I selected DJI_Chip and clicked Next.
I learned this next sequence from watching a youtube video that I found.
I clicked Unseal / Boot, then Read Chip Info.
Then I clicked Clear Chip Errors. Then Unseal / Boot again, Read Chip Info again, to verify that the 550066 error was now cleared 0x000000 and then clicked Seal / Exit Boot to seal the battery. If the battery is not Sealed, then the drone will not be able to recognize it and it will not work.
When you are finished click End Reset.
Next, I was able to charge the battery with the DJI Charger. I allowed the battery to fully charge and now it is functioning again.
Next, I checked the individual Cell voltage difference in the DJI app.
There was still a little bit of a voltage difference in the Cells. I learned on the forum from @djibattworkshop (an expert in repairing DJI batteries) that fine balancing should be done at full charge.
I started this repair with no knowledge of how to repair a battery and no knowledge of how the NLBA software worked. In the end, I was able to take a battery that was completely dead, apply 12V to wake it up, determine that Cell 3 was bad, balance the Cells voltages, clear the fault code and get it back fully functioning.
With just a basic understanding of voltage and current, how to use a multi-meter and DC Power Supply it is possible to do these battery resets because the NLBA software and NLBA1 device fill in the gaps and provides the battery data that you need. However, I would caution you, if you are new to this to use the forum and ask questions to gain understanding before doing anything you are not sure about.
But in all this was a great investment and I am very appreciative of the community on the forum and all the help I received.