Hello,
On the DJI mini 2 manual I can see that it's recommended to store the battery near an amount of less 30% battery...
So I can store my battery at a percentage of 15 % and it will be okay ? I don't understand the user guide...
What can I do to keep my brand new battery safe and healthy ?
Cordially.

Put each battery in the drone and check battery info in the app.  You're aiming for 3.75 - 3.8V per cell if they're not going to be used for a few days.
Google "lipo storage" or "lipo safety" for more information and safety warnings.
Generally, never store them at full charge or below 3.2V.

Your battery will automatically discharge to storage voltage without you doing anything.

I have always fully charged my batteries after a flight session. I have been flying about 3 or 4 years now, not had a battery fail yet, as Labroides said, they discharge to a storage amount anyway, after about 24 hrs they drop to about 94/96%, after about 10 days they will drop to about 70/75%, granted, this isn't long term storage %, if its going to be longer than a few months then drop them to about 30% BUT check on them regularly to make sure they do not get too low, what you don't need is for them to fully empty as you will more than likely have killed it/them.

I have used the work "about" because i cannot quite remember the % but i am sure i am very close, its 3:30am and i can not be asked to go looking for the exact figures

Okay thanks guys ! So I'll charge them and let them automatically discharge now

Hi there. Thank you for reaching out. We're glad that our fellow DJI Pilots here have already clarified your query.
You may also refer to the image below for some additional information about battery storage. Thank you for your valued support.

Labroides Posted at 2-18 15:46
Your battery will automatically discharge to storage voltage without you doing anything.

Hopefully!

Check that they are auto discharging before relying on this.

I had two batteries replaced by DJI (from a fly more combo) that did not discharge when left out of the drone or charging hub.

Leaving them for two weeks connected to nothing they were still at 96% charge. According to the manual they should have been down to 72% after 9 days.

They were replaced as "defective".

At least one of the two replacements DOES auto discharge when not connected to anything. I've yet to try them in the hub.

So it seems that there could be a batch out there with a faulty control board.

No Original Thought Posted at 2-19 03:11
Hopefully!

Check that they are auto discharging before relying on this.

Its cause the needed the firmware updated, i had 2 of mine like that, i updated the firmware in the settings and all was well  

Bashy Posted at 2-19 04:35
Its cause the needed the firmware updated, i had 2 of mine like that, i updated the firmware in the settings and all was well

When I updated the drone firmware one battery was in the drone.  I assume that battery's firmware was updated too.   But I don't see how to update the firmware of the second battery.  When the second battery is in the drone and I try to update the drone firmware it says software is up to date.  I don't see a place to update just the battery firmware.

Bashy Posted at 2-19 04:35
Its cause the needed the firmware updated, i had 2 of mine like that, i updated the firmware in the settings and all was well

The firmware would not update...

I tried with the Fly app and with DJI Assistant, downgrading the aircraft multiple times and then upgrading again to v1.03.00... at no point was I ever getting the prompt that the batteries were being upgraded. There is another thread suffragette where o go into the full detail of it. I'll update that thread when I find it.

Also, the firmware upgrade was to address the problem of the batteries not auto discharging when they were in the aircraft or charging hub. Mine were not discharging when they were not connected you anything.

Here is a summary of battery info:
The controller uses Li-ion batteries, not as sensitive as LiPo.
The drone uses LiPo batteries.

Battery charge level:
All four LED lights are on – the battery is at 88 percent or over
The first three LED lights are on but the fourth one is flashing – the battery is between 75 and 88 percent
The first three LED lights are on but the fourth one is not – the battery is between 63 and 75 percent
The first two LED lights are on, the third one is flashing, but the fourth light is off – the battery is between 50 and 63 percent
The first two LED lights are on but the third and fourth lights are not – the battery is between 38 and 50 percent
The first LED light is on, the second light is flashing, and the third and fourth light is off – the battery is between 25 and 38 percent
The first LED light is on but the other three are not – the battery is between 13 and 25 percent
The first light is flashing and the other three LEDs are off – the battery is between zero and 13 percent

LiPo Battery Features
1. Balanced Charging: during charging, the voltages of the battery cells are automatically balanced.
2. Auto-Discharging Function: to prevent swelling, the battery automatically discharges to approx. 96%
of the battery level when it is idle for one day, and automatically discharges to approx. 72% of the
battery level when it is idle for nine days. It is normal to feel moderate heat being emitted from the
battery during the discharging process.
3. Overcharge Protection: the battery stops charging automatically once fully charged.
4. Temperature Detection: To prevent damage, the battery only charges when the temperature is
between 5° and 40° C (41° and 104° F). Charging stops automatically if the temperature of the
battery exceeds 50° C (122° F) during the charging process.
5. Overcurrent Protection: the battery stops charging if an excess current is detected.
6. Over-discharge Protection: discharging stops automatically to prevent excess discharge when the
battery is not in flight use. Over-discharge protection is not enabled when the battery is in flight use.
7. Short Circuit Protection: the power supply is automatically cut if a short circuit is detected.
8. Battery Cell Damage Protection: DJI Fly displays a warning prompt when a damaged battery cell is
detected.
9. Hibernation Mode: if the battery cell voltage is lower than 3.0 V or the battery level is less than 10%,
the battery enters Hibernation mode to prevent over-discharge. Charge the battery to wake it from
hibernation.
10. Communication: information about the voltage, capacity, and current of the battery is transmitted to
the aircraft.

FlyingOverABQ Posted at 2-19 20:22
When I updated the drone firmware one battery was in the drone.  I assume that battery's firmware was updated too.   But I don't see how to update the firmware of the second battery.  When the second battery is in the drone and I try to update the drone firmware it says software is up to date.  I don't see a place to update just the battery firmware.

Its in the settings somewhere, it will say battery firmware, that's how i did it

Nowhere in any menu is there any indication of battery firmware version nor an update/check button. DJI lazy again as always!

Johnny_J Posted at 2-20 07:55
Nowhere in any menu is there any indication of battery firmware version nor an update/check button. DJI lazy again as always!

Instead of just constantly whining about DJI's work ethic, why don't you head over to the developer forums and suggest they add this functionality?

Bashy Posted at 2-20 07:51
Its in the settings somewhere, it will say battery firmware, that's how i did it

I and Johnny_I can't find it.

Bashy Posted at 2-20 07:51
Its in the settings somewhere, it will say battery firmware, that's how i did it

I've never seen that option in either the Fly app or DJI Assistant.

Can you direct to exactly where that option is and/or post a screenshot?

I also asked DJI support how I can check the battery firmware and they said that there was no way, currently.

blue_canyon21 Posted at 2-20 10:19
Instead of just constantly whining about DJI's work ethic, why don't you head over to the developer forums and suggest they add this functionality?

Are they more responsive in that forum, or do you just get the same stock answers?

Maybe I'll pop over and have a check...

No Original Thought Posted at 2-20 13:38
Are they more responsive in that forum, or do you just get the same stock answers?

Maybe I'll pop over and have a check...

When I was asking about the SDK release, they were quite responsive.

When I gave feedback on some Pro mode camera settings not working, they responded in a few days and it was fixed in the next version.

With all the very latest firmware updates, the battery in my Mini2 functions as follows:

From a full charge, automatically depletes itself to 96 percent after 24 hrs of non-use.  

After 5 days, automatically depletes itself to 70 percent during the same non-use period.   

djiuser_A8aeRUwNBtkb Posted at 2-20 17:08
With all the very latest firmware updates, the battery in my Mini2 functions as follows:

From a full charge, automatically depletes itself to 96 percent after 24 hrs of non-use.  

That should be 70% after 9 days for the mini 2

No Original Thought Posted at 2-20 13:36
I've never seen that option in either the Fly app or DJI Assistant.

Can you direct to exactly where that option is and/or post a screenshot?

I think It's in the same section where you update everything else (About), i think, i forget now, makes sense though, if the battery needs updating then it will show in there, if it does not, i am not sure if it shows or not, i cannot remember but its deffo there if it needs doing, 100%
Either that or it pops up on the splash screen where it tells you to update everything else, i really cannot remember now to be honest, i did it months ago for 2 batteries, the other 2 did themselves i believe.

Bashy Posted at 2-20 19:20
I think It's in the same section where you update everything else (About), i think, i forget now, makes sense though, if the battery needs updating then it will show in there, if it does not, i am not sure if it shows or not, i cannot remember but its deffo there if it needs doing, 100%
Either that or it pops up on the splash screen where it tells you to update everything else, i really cannot remember now to be honest, i did it months ago for 2 batteries, the other 2 did themselves i believe.

There is supposed to be the popup message on the opening screen of the app, top left corner in something like a message bubble...

I had that pop up for the aircraft firmware update, but _never_ for my batteries.

I know other did see that popup for their batteries, but that is my point - it doesn't seem to be reliable.

One argument was that as I bought.ky combo in November last year - 5 months after the firmware update was released - maybe my batteries were already up to date. Well, the aircraft wasn't and also my batteries were not discharging either in or out of the charging hub, so something was not right.

There is no entry in the about screen or the battery info screen for battery firmware.

Bashy Posted at 2-20 19:16
That should be 70% after 9 days for the mini 2

I've read that too, but my Mini 2 battery stays at 96 percent for five days then discharges to 70 percent after day 5.   I wonder if we are using the same firmware update.