March 28, 2022
If you’ve ever shopped for an extra battery for your DJI drone online you may have noticed the phrase “Intelligent Flight Battery” in the title of the listing. This isn’t just a marketing ploy (even if it does sound a little pretentious) This phrase is referencing the use of a Battery Management System chip and firmware imbedded in all DJI battery packs (going back to the Phantom 2 series). It’s responsible for alerting the pilot when it’s time to land and safely discharging and storing your expensive battery. It’s also rendered thousands of DJI batteries completely useless due to a bug in the firmware…
Before we dive in to the issue at hand, let’s discuss some of the basics of a LiPo battery and how they relate to drones. There are several factors to consider when trying to determine peak efficiency but the main two will always be Capacity (measured in MAH or MilliAmps per Hour) and Cell count (denoted by the number of Cells in a series next to the letter “s”). Each standard cell will provide 4.2 - 4.4v volts at full charge and will have varying capacities determined by the manufacturer. For example, a battery pack for the Mavic 2 is a 3850mah 4s (4 cells in a Series) so it will have a max charge voltage of around 17.6 volts (4.4volts per cell x 4 cells) and the pack will provide 3850 milliamps per hour or 3.85 amps per hour.
Most drones will draw 10-20 amps PER MOTOR during flight, meaning an average drone in flight is drawing 40-80 amps. This is why drones can’t typically fly for more than 20-25 minutes at a time. In order to increase the capacity of the battery you have to increase the size and mass of the cell (so physically larger batteries will have a larger MAH capacity but they’re heavier.) This is why increasing the size and capacity of the battery doesn’t always make things more efficient. The heavier your drone is, the harder the motors will have to work to lift the drone, which in turn increases the amp draw for each motor. Heavy drones also tend to have poor flight characteristics. When commercial drone makers design a battery they do so with efficiency in mind and try to find that happy medium of long flight time and good flight characteristics.
The last thing that is worth mentioning when dealing with LiPo’s as they relate to drones is the charge and discharge rate or C-rating of a battery. We won’t bother with the formula and we’re not going to delve too deeply here as DJI doesn’t even publish their C-ratings, but the C-rating will tell us how many amps can be safely drawn from a battery in short amount of time. This is crucial for drone users as most drones will draw a lot of amps very quickly and batteries that are over drawn past their given C-rating will usually become puffy or swollen and will most certainly have diminished performance and flight time. C-Ratings are determined by the quality of components used and tied to the size of the battery (the more capacity the easier it is to achieve a higher C-rating.) If your battery is puffy or swollen it’s time to recycle it or relegate it to a bench pack, there’s not much you can do short of replacing the cells if you want to use it again for a flight pack.
So why won’t my battery charge, it’s not puffy or swollen?
LiPo Batteries are lazy. They don’t want to hang out at full charge and they don’t want to sit on empty. Most manufacturers and keyboard warriors recommend leaving your batteries at 30%-40% for storage. But, if you leave your LiPo battery at full charge for more than a few weeks at a time, or discharge it below 3.2v then you’ll most likely compromise your batteries overall storage capacity. This will quickly effect that aforementioned C-rating and your chances of over-drawing your battery will be much higher. This is where the “intelligent” aspect of your “intelligent flight battery” kicks in. On every DJI battery pack there is a BMS chip that provides much needed telemetry data to your mainboard and displays it on the battery tab of the DJI app. This data is used to estimate your overall remaining flight time, monitor cell integrity and keep an eye on the temperature of the pack, and it does this with safety in mind. In addition to providing telemetry the BMS chip will also regulate the self storage and discharge cycles of your battery. If you leave a DJI battery at full charge for 10 days then your battery will automatically begin to discharge to a safe 30% capacity for storage. Neat!
Here’s where the trouble begins for a lot of DJI users.
There’s a bug that will discharge your cells to 3.2v per cell or “true 0%” capacity when in self storage or self discharge mode. Not neat…
Yep, that’s right. There’s a bug in the firmware of DJI batteries that will render them useless if you don’t use them (where have we heard that before?). If you’ve left your battery in storage for a while and it won’t take a charge anymore, chances are it’s due to this bug. Once the BMS chip detects a cell below 3.2v it will trigger a “power failure” and keep your battery from taking a charge (even if you bypass the chip and manually charge this battery up to 4.2v per cell). If your battery drops below 3.2v per cell naturally (like a broken cell) then you have a bad battery, this is why the error code triggers a power failure on the chip and doesn’t allow the battery to be used. However, since this power failure was the result of a good battery discharging too bug, the physical cells of your battery are usually still good and should still take a full charge if you get the error cleared quick enough. The longer the battery stays in the error state below 3.2v per cell, the higher the chance of damaging or limiting the capacity on your battery.
This is where we can help!
If you have a physically good battery that doesn’t charge anymore, send it to us and we’ll interrogate it for free (shipping fees sill apply). If the voltage hasn’t dropped too far we can clear the error and test the cells to make sure everything is back to normal.
We can currently communicate with the BMS chip and offer repairs with free interrogation on the following models of DJI Batteries;
Mavic Air 2
If we determine that your battery can be saved, we can clear the error, charge the battery and ensure that capacity is close to manufacturer tolerances. To get this process started and generate a prepaid label, select “repair my drone” and select the drone model, then “battery repair” from our website.