This is a clear indication of a high resistance connection and a resulting intermittent arc while voltage was applied to those terminals (identified as hi dc by OMM). This happens a lot in similar battery systems including those for other portable electronics (laptops, games systems, tablets, battery or juice packs,etc.) and typically happens where the conductor forms a bend as that is a stress point that may fracture or partially separate (which creates the area of high resistance, which also generates heat - think of your radiant electric range coils). Even DC at these voltages can generate sufficient temps to ignite both the plastic case and nearby ordinary combustibles. While you have the charger take another look for any artifact or damage around the contact pins (beading, deformity, areas where it looks eaten away at all). This can be done with a macro close up photo and magnifier. It is hard to tell from your photos but the fault looks to be in the case of the battery as opposed to a fault on the pins that are exposed.
The only way to definitively look at the specific point of failure is to xray the damaged component and also a working one (exemplar) to look for the fault. If this caused damage to your home, your insurance carrier would likely pay an electrical engineer to conduct a lab exam to identify the failure point and pursue cost recovery from the manufacturer. Thankfully this does not seem to be the case here.
Fortunately you were not injured and your home was not damaged, but this is a really clear example of the need to think about where you charge and store your gear, and make sure that while charging you are in attendance and aware of what is happening. While some aftermarket case manufacturers advertise the feature of "charge in case" (I own one - great case) not so sure that is a prudent move as if this were to occur and the charger is surrounded by the foam insert, the heat has no place to go and it would likely have ignited and been much more exciting.
This is almost serious enough that you might wish to consider notifying the CPSC (consumer protection safety commision) who is responsible for initiating recalls of defective components that present a risk of injury or loss of life. If this happened and it ignited your home, the result could have been tragic. DJI should respond aggressively and want the component back and will likely also want the charger (both components need to be looked at to see the problem in their totality). You can file a report with them online (cpsc.gov) all this does is add your experience to the database so that if there are cluster appropriate action can be taken to help keep others safe.
For the rest of the community that has a mini, let's be especially vigilant and careful until a definitive finding as to WHY this happened is arrived at.
Some suggestions:
- ONLY charge on non-combustible surfaces in an open area (not on the bed, not on carpet, not in the case, not in the car unless your present)
- MONITOR your charging: do not plug and leave it overnight or in the garage/closet/basement where you cant see, hear, smell the unit charging.
- INSPECT connectors for damage, oxidation, moisture, corrosion, etc.
I see MANY fires in residences and vehicles where the root cause is a defective battery component and/or charger such as this (even on very high quality high end devices), so it is not as uncommon as you think.
Be safe and thank you for sharing your experience. We can all learn and profit from it.
