Battery cells under voltage

[Dmascot]

I received a warning “battery cells under voltage, replace battery” this morning while flying my Mavic Mini. I received the warning at 30% battery, 470 m from home, two minutes later just before landing the battery was down to 20% with the message “low battery return to home promptly”.
That message seemed odd too, considering how close I was to home. Seems I should get at least 5% more usage that close to home. Bummer getting these warnings because I was able to go 1100 m on this flight. Actually broke 1000m Hope my battery isn’t toast. I have been using my iPhone charger to charge the battery. I didn’t get a charger with my Mini.
.

 

[paulatkin73]

when you draw max current from the lipo battery its voltage 'sags' and goes sometime quite low. if you were in sport mode drawing 15A or so - it may have been the case. flight controller software usually takes to account the sag effect and starts showing warning only if voltage drop lasts. generally, it is not a great idea to draw maximum current from the lipo if you have only 20% of capacity left. means - switch to P mode and fly back slower when it complaints about the voltage level.

 

[Dmascot]

when you draw max current from the lipo battery its voltage 'sags' and goes sometime quite low. if you were in sport mode drawing 15A or so - it may have been the case. flight controller software usually takes to account the sag effect and starts showing warning only if voltage drop lasts. generally, it is not a great idea to draw maximum current from the lipo if you have only 20% of capacity left. means - switch to P mode and fly back slower when it complaints about the voltage level.

Thanks, I was in sport mode. And it was cold too.

 

[DanMan32]

"Low Battery, return to home promptly" at 20% is normal. It wants to give you time to get back.

Battery management and alerts are different in MM than on other DJI quads.
I never got a forced landing but was warned getting it near 0 could damage the battery. So do plan to land, not just return home, before 10%.

 

[old man mavic]

something that everybody is forgetting with the MM flight batteries ,apart from being a different type to all the other batteries used in the mavic stable,there are two factors at play, one is the temperature at this time of year in the northern hemisphere for the most part cold, and we need to consider not pushing the batteries to their limits by discharging them to very low limits, treat them with care and they will last longer

 

[DanMan32]

Not an issue here. To us it's cold, but to many of you it's just cool.

 

[est73]

I got the same error today while pushing the MM full stick in sport mode the entire flight. I checked airdata and for some reason, the message was not in the logs.

Here is the data from when the message showed up...

Flight time	Baro. Alt.	Sonar Alt.	Speed	Home Dist	Bat%	Volts	Cell 1	Cell 2
13m 08.2s	267.7ft	43.6ft	12.3mph	738.4ft	0.26	6.60V	3.300V	3.302V
13m 08.6s	272.0ft	43.6ft	12.5mph	745.6ft	0.26	6.58V	3.294V	3.286V
13m 09.0s	276.6ft	43.6ft	12.5mph	753.0ft	0.26	6.58V	3.294V	3.286V
13m 09.4s	281.2ft	43.6ft	12.5mph	760.3ft	0.26	6.58V	3.294V	3.286V
13m 09.8s	285.4ft	43.6ft	11.9mph	767.4ft	0.26	6.61V	3.301V	3.304V
13m 10.2s	288.4ft	43.6ft	9.6mph	773.6ft	0.26	6.61V	3.301V	3.304V
13m 10.6s	290.0ft	43.6ft	6.6mph	778.1ft	0.26	6.74V	3.394V	3.398V

 

[paulatkin73]

I got the same error today while pushing the MM full stick in sport mode the entire flight. I checked airdata and for some reason, the message was not in the logs.

Here is the data from when the message showed up...

Flight time	Baro. Alt.	Sonar Alt.	Speed	Home Dist	Bat%	Volts	Cell 1	Cell 2
13m 08.2s	267.7ft	43.6ft	12.3mph	738.4ft	0.26	6.60V	3.300V	3.302V
13m 08.6s	272.0ft	43.6ft	12.5mph	745.6ft	0.26	6.58V	3.294V	3.286V
13m 09.0s	276.6ft	43.6ft	12.5mph	753.0ft	0.26	6.58V	3.294V	3.286V
13m 09.4s	281.2ft	43.6ft	12.5mph	760.3ft	0.26	6.58V	3.294V	3.286V
13m 09.8s	285.4ft	43.6ft	11.9mph	767.4ft	0.26	6.61V	3.301V	3.304V
13m 10.2s	288.4ft	43.6ft	9.6mph	773.6ft	0.26	6.61V	3.301V	3.304V
13m 10.6s	290.0ft	43.6ft	6.6mph	778.1ft	0.26	6.74V	3.394V	3.398V

this log is not quite helpful, try to see if you have .DAT log file in the phone/tablet directories and look at it. you need to look at current and voltage graphs at the time of the warning. it was probably a momentary sag of voltage level lower than 3v per cell. log shown above probably does not have a grain fine enough to show that.

 

[est73]

I don't know... that table is straight from the log file. I just removed the unnecessary fields.

 

[Pedro1983]

Did this happen to me once the battery may be damaged? I'm worried. Comment after other flights

 

[Thomas B]

¿Esto me sucedió una vez que la batería puede estar dañada? Estoy preocupado. Comentario después de otros vuelos

Translation: Did this happen to me once the battery may be damaged? I'm worried. Comment after other flights

El idioma oficial del foro es el inglés. Por favor úsalo. Google Translate puede ayudar
Translation: The official language of the forum is English. Please use it. Google Translate can help

 

[WithTheBirds]

You can be confident there is nothing wrong with the battery- take a little time to get yourself up to speed with the performance characteristics of LiION cell chemistry and you will appreciate what was going on. Low temperature + reduced V with lowering SOC + increased current demand = the battery management smarts in our mavics can be smarter than us- giving you every opportunity to avoid failure in flight.

 

[Ger]

Hovering just around freezing here. Was wondering how this would affect the new type of bats in this drone. I noticed today that the speed of my mini will get slower as the battery starts to drain. Anyone else notice this?

 

[Back Country]

Interesting observation. I'veonly hsd opportunity to get mine out twice now, both times right around 0 degrees Celcius so I don't have experience with the batteries at a different temperature for reference but it is starting to finally get cold here again so I'll likely have mine out in -10 to -20 temps in the next little bit, I'll have to see how the battery charge and drone speeds are comparatively vs. at zero degrees C.

 

[WithTheBirds]

Interesting observation. I'veonly hsd opportunity to get mine out twice now, both times right around 0 degrees Celcius so I don't have experience with the batteries at a different temperature for reference but it is starting to finally get cold here again so I'll likely have mine out in -10 to -20 temps in the next little bit, I'll have to see how the battery charge and drone speeds are comparatively vs. at zero degrees C.

It is likely the battery electronics will protect the cells- as a general rule LiION should not be charged below 5degC and will likely be permanently damaged below 0degC. You should also expect less performance at lower temperatures. Keep the batteries in your pockets close to your skin before flying if it is really cold.

 

[Back Country]

It is likely the battery electronics will protect the cells- as a general rule LiION should not be charged below 5degC and will likely be permanently damaged below 0degC. You should also expect less performance at lower temperatures. Keep the batteries in your pockets close to your skin before flying if it is really cold.

Thanks, that is more or less what I was thinking, batteries in an interior jacket pocket, or maybe slip a hand warmer in the Fly More case on top of the battery hub as there is quite a bit of room there.

Do you think the current flow from discharge during actual flight will keep the batteries warm enough to not be damaged if I can manage to keep them warm during transit? I live in an area that see temps below feeezing regularly from Oct.(Sept. frequently as well) all the way to April. Hoping I don't have to cherry pick the warm days only, that won't work well for getting pics and video while ski touring, ice climbing, and winter camping like I had hoped to do.

 

[DanMan32]

Hard to say if generated heat would keep up with heat dissipation, particularly in flight. Battery stat details shows battery temp as well as cell voltages.

 

[WithTheBirds]

Thanks, that is more or less what I was thinking, batteries in an interior jacket pocket, or maybe slip a hand warmer in the Fly More case on top of the battery hub as there is quite a bit of room there.

Do you think the current flow from discharge during actual flight will keep the batteries warm enough to not be damaged if I can manage to keep them warm during transit? I live in an area that see temps below feeezing regularly from Oct.(Sept. frequently as well) all the way to April. Hoping I don't have to cherry pick the warm days only, that won't work well for getting pics and video while ski touring, ice climbing, and winter camping like I had hoped to do.

Yes. You will get slightly reduced run time if the temp doesn't reach 20 degC however the self heating effect will work well for you- internal resistance is highest at full SOC and reduced temp. Higher internal resistance = more heat during discharge.

 

[DanMan32]

But internal resistance will also cause increased voltage sag at high currents.