Battery Charger

Shawgod

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I have the Phantom 4 Pro DJI battery Charger which charges 3 batteries. I have three batteries on it and put the charger into storage mode. All three lights are blue now. I know that means that they are in storage mode. Being that it is winter I am not flying the drone through the winter months, will the batteries be fine in the spring time? I just want to make sure that my batteries don’t turn into three bricks.
 
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Should be fine if that blue light means that the batteries are charged somewhere around 60%.
 
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Just as a matter of interest, anything you need to be aware of to get them out of hibernation mode?
 
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I can't speak about the P4 batteries and how their hibernation mode works but I can say it's a hit and miss with P2 and P3 batteries trying to revive them once they have gone into hibernation. My advice is not to test it. I recommend checking your batteries at least once per month. They will self discharge to a safe level automatically if stored fully charged. I check on my P3P once a month if not flying, fully charge all batteries and I'll set up the aircraft and start the props to keep all the Nand chips alive and well. These birds don't like to sit inactive for long periods of time in my experience. I've had it for years with no issues or battery problems.
 
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I have a Phantom 4. I try to keep the batteries around 30%. If I charge them up to fly and don't use them that day the next day I fly them down to 30%. Is this right?
 
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It's OK.
But, I don't know why 30%. Common agreement is around 60%.
 
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Li-Po battery cells have 4.1V when fully charged, 3.5 V when fully discharged. Now:
* Such cells will release hydrogen, swelling and damaging the cells; they do that very slowly when not fully charged, but the release rate can increase by two magnitudes when fully charged. That's why the battery IC (Battery Management System) will auto-discharge it to 60%, or circa 3.8 V.
* The cells will slowly discharge, due to their chemical balance, and due to the electronics requiring some miniscule current. So keeping the cells at 30% would really mean you have to check them each month. But keep them at 60%, and it will take over 3 months to self-discharge them - then you only need to recharge them once per season.
* When fully discharged, voltage of the battery will start to drop below 3.5V. If it drops to 3.1V per cell, nothing that bad should happen, the battery will take up to few hours to recover but will recover. But if it drops below 3 V, it might have effect on the chemical separation - the electrolyte, rather than keeping the electrodes stable, will start dissolving copper atoms and depositing them somewhere else. Depending on type of electrolyte, it may also crystalize or become thicker in parts of the cell. This will increase self-discharge current and the cell will drop voltage even faster.
* To avoid flying with damaged cells, the IC controlling the battery(Battery Management System) verifies its voltage. When it detects a cell has below 3V, the BMS will raise "Permanent Failure" flag. When this flag is raised, the BMS will no longer allow to charge or turn on the battery. Permanently.
* There are software ways to remove that PF flag, but if it was raised, then it is likely that the cells are damaged - they are probably still ok to use as power bank for your phone or other low-power tasks, but flying with such a battery can lead to sudden power drop or a fire. It is possible to re-charge and unlock a battery which cells went as low as 0.5V - but then, you've lost almost half of the battery capacity, and the self-discharge rate of such cells is so high that 3 months may be enough to drain it completely.

Also note that temperature is a factor. The battery will self-discharge slower and release the hydrogen slower in low temperatures. Unless in reaches 0 deg Celsius, then each time the electrolyte starts to solidify the battery will discharge a bit to get it back to fluid/gel state. So freezing temperatures for prolonged periods are bad (though the freezing point is really below 0, it depends on the specific electrolyte used).

The voltages I provided are for no load case. When under a load, the voltage drops.
 
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AWD

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Thanks for the excellent explanation of what's going on with the batteries.

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