DJI Inspire One Battery Revival…

As i am sure you are aware batteries for the DJI Inspire One do not come cheap (£135.78 at time of writing this in the UK, $170USD), so imagine my annoyance when after a period of storage one of my TB47’s with only 6 cycles displayed a low voltage balance on one cell and refused to charge on the standard DJI charger, it’s sitting there teasing me with a double flash on the third LED when trying to power it on and showing a warning on the DJI Go app telling me it’s had it…

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But once a battery is out of warranty you have no chance getting any help from DJI even on a low usage battery…

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Here you can see the 4th cell showing 4.04v, still a healthy voltage, but obviously too low for the DJI electronics to allow it to balance so without intervention this battery is toast!

**Attempt this at your own risk**

So before disposing of it i’d see if i could rescue it just by bringing up that single cell a small amount…

To do this I removed the battery top cover…

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Once removed you can see a small white 7 pin multiplug (DF13-7S), this is the Li-Po balance connector to the DJI balance board, through this you can access the individual cells. These connectors are on the small side, and finding a prewired 7 way connector proved impossible but luckily I had a pre wired 6 pin connector from another project…

So i soldered this to some header pins and connected it to the far left of the plug (looking at the front of the battery) and began working my way through to find the low individual cell…

Looking from the front of the battery they are laid out Left to Right, cells 1-6…

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To check each cell individually the pins are connected to the battery as follows (From Left to Right looking at the front of the battery)…

 

Pin 1: Cell 1 -Ve

Pin 2: Cell 1 +Ve / Cell 2 -Ve

Pin3: Cell 2 +Ve / Cell 3 -Ve

Pin 4: Cell 3 +Ve / Cell 4 -Ve

Pin 5: Cell 4 +Ve / Cell 5 -Ve

Pin 6: Cell 5 + Ve / Cell 6 -Ve

Pin 7: Cell 6 + Ve

So working across the cells, Pins 1 & 2 are cell 1, Pins 2 & 3 are cell 2, Pins 3 & 4 are cell 3, Pins 4 & 5 are cell 4, Pins 5 & 6 are cell 5 and Pins 6 & 7 are cell 6.

Working through these with my meter, i found all the cells to be 4.18v with the exception of cell 4 which was 3.94v, not really that far out of balance at all, i’ve seen and rescued far worse than a voltage difference of 0.22v.

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I then used a couple of jumper cables to connect cell 4 to some screw terminals on a bread board…

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I then screwed cables with 4mm banana plugs in to the screw terminals and connected them to my iCharger.

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The iCharger was set to Li-po Charge, Single cell (1S), and .5A charge rate (charging through very thin cables here)…

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The charge was started, I kept it monitored throughout…

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I stopped the charge after an hour to check progress, the battery had taken 344mah at this stage and voltage had settled at 4.05v, no abnormalities in charging, no heat at all in the cables, so i restarted the charger to let it run its course…

As the charge reaches the end the charge current drops, after another 1:30 the charge current was down to .13A and another 287mah had been put in to the cell, giving it a resting voltage on my meter of 4.12v, thats better…

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What I hadn’t anticipated was that the DJI circuitry within the battery would now assume the battery was flat, so even though I knew the battery was charged and the DJI app showed the voltages as correct, it showed the mah capacity as 200 and that there was no available flight time…

To combat this, discharging the battery to zero is the way i assume i need to go so that it can then be charged on the DJI charger…

With that in mind I really wanted to perform a controlled discharge keeping the cells monitored, so i went to the effort of rigging up a 7th pin on the connector so i could monitor each cell during this process… (I have ordered the correct connectors to make this easier in the future)…

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So while thinking of doing a discharge, i thought it might be an idea now i have made a complete balance lead and connected directly to the battery to do a couple of charge/discharge cycles on the pack and see how it fairs, as that will tell me if that cell is trash or not…

 

Starting with a full balance charge, it took a while to get cell 4 up to match all the others, but then it always does when one cell is out of balance by more than 0.01-0.02v…

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But the end result is just fine and has left a nicely balanced pack, time for bed so i’ll leave it to settle over night and check it again in the morning before performing a discharge…

And after 6 hours rest all cells are still holding voltage and balance, this is good news…

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The charger was then set to do a cycle discharging to 3.30v then waiting 5 minutes before balance charging to 4.20v again.

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The discharge pulled 3978mah from the pack, this is a healthy figure…

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And after 5 minutes rest all cells were within .1v of each other, again a nice healthy figure, with cell 4. ‘the dead cell’ joint highest with cell 2.

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Then the charge cycle began, all cells reached within 0.01v at the same time, the end result being… 3681mah put back in, this is less than that taken out as the battery had time to recover between the discharge and then charge…

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And again we are showing a nicely balanced pack…

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The battery was then left sitting for 10 minutes before being discharged again, all going well on this discharge then the batter will be reassembled and a charge attempted on the DJI charger, this time I discharged to 3.1v which once the load is removed and the battery settled should leave all cells sitting around 3.3v…

These are the cell voltages while still under load at the end of the discharge…

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Now these may seem low but as soon as the load was removed and the pack given a chance to settle they bounced back to this, not bad at all and the ‘bad cell’ is now the one which has held it’s voltage the best, go figure…

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I also checked the cell resistance, not bad across the board and again the ‘bad cell’ is actually not ‘bad’ at all…

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Reconnected the DJI circuitry and the battery is flashing the first light for a flat battery, which is correct…

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Now reassembled and connected to the DJI charger, first light is flashing for charging, no 3rd light warning anywhere to be seen…

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Fresh of the DJI charger, this is good news… 4 lights indicating fully charged…

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And a quick power up in the Inspire One to check the figures in the DJI Go app…

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The end result is what you would expect to see on a normal well balanced battery, weather and time permitting i’ll give it a flight test tomorrow but it’s been cycled a couple of times and performed fine in that environment, a test flight will just confirm it is still ok at higher loads…

All in all very pleased with the result, a little bit of tinkering and save £135 for a replacement battery…

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