Voltage drop, low battery warning, end of battery life?

[dimizu]

Hi all. I hope here is a log expert how can give me an advice.

Since years ago, I had a scary situation with a dji mavic air 1 (battery from 65% immediately to 0 % and force landing) now with the air 2s I would be a little more careful on battery health.

I wonder if there are any indicators in the log files that can indicate that a battery is coming to the end and it would be better to replace it.

My batteries have about 72 charge cycles and are 3 years old. I usually charge them in the evening and then go into the mountains the next day.

Here a log:
DJI Flight Log Viewer - PhantomHelp.com


The battery starts at 93% (strange?), but after a few seconds the voltage drops to 3.28 volts. Now I am a bit worried about this significant drop in voltage.

I checked other logs. I often see this behaviour in the last logs. On one occasion there was even a warning: "The battery power limit will automatically reduce the aircraft's manoeuvrability to ensure flight safety".

Often after 1 or 2 minutes (perhaps after the battery goes warmer) of flight the voltage returns to better values.

What do the experts mean? Why it happens. It is a sign that the battery is at the end of its life and it is better to replace it. Or is this normal? I have looked at older logs and I do not see this significant voltage drop after start.

Is there any general indication (even if I don't see voltage drops) when a battery is at the end of its life?

Thanks in advange for advice to better understand logs<->Battery Health

 

[GFields]

Is this happening with all batteries?

 

[dimizu]

I would say yes. Not so extreme with this one, but yes. I have 3 batteries that are all 3 years old. 2 have 72 charge cycles and 1 has 64 charge cycles. The one with 64 cycles is not so bad.

 

[GFields]

If they have not been properly manged they could be going, if not already, bad. I wouldn't change using them to fly.

 

[dimizu]

So you would say that this voltage drop is acceptable?
In the case of the log provided, I can understand that. Because it was a winter day, but sunny. The battery started with a temperature of 49.5 F.
But I have another log file where the voltage drop even caused a battery power warning. In this case the battery started at a temperature of 58.5 F.

But again, the battery did better during the flight.
It is a little frightening that the problems occur at the start. I would say this is a sub-optimal battery, so I only fly from 100-50%. But with these problems at take off this is not a solution.
I am a little worried about finding the ideal time to change the battery. So I look for parameters in the logs that tell me: now is better not to fly any more.

 

[Dbez1]

Below the final post in this thread, you will find a category called “similar threads” where the issue has already been discussed. Maybe you will get more feedback there. Best wishes.

 

[kenjancef]

Buy a new battery, see if it still happens. Or if someone in your area has an Air 2S, use one of their batteries.

 

[dimizu]

Below the final post in this thread, you will find a category called “similar threads” where the issue has already been discussed. Maybe you will get more feedback there. Best wishes.

Thanks

 

[dimizu]

Buy a new battery, see if it still happens. Or if someone in your area has an Air 2S, use one of their batteries.

In older logs, when the battery was a bit younger, this did not happen. So I think the battery is ageing and now I am looking for indicators as to when should I replace it...

 

[Meta4]

The battery starts at 93% (strange?)

How recently was the battery charged?
It looks like the battery had been partially discharging after charging some days earlier?
You should always start a flight with a fully charged battery.

but after a few seconds the voltage drops to 3.28 volts. Now I am a bit worried about this significant drop in voltage.

The reason the voltage drops there, is that you were climbing at full throttle.
That always puts a big load on the battery and it will recover after you ease up on the throttle.

On one occasion there was even a warning: "The battery power limit will automatically reduce the aircraft's manoeuvrability to ensure flight safety".

That will show if you run the battery down to critical low voltage level and are trying to fly hard.

Often after 1 or 2 minutes (perhaps after the battery goes warmer) of flight the voltage returns to better values.

It's not a temperature thing, it because you eased up on the throttle.

 

[dimizu]

How recently was the battery charged?
It looks like the battery had been partially discharging after charging some days earlier?
You should always start a flight with a fully charged battery.

I usually charge the night before and head out to the mountains the next day. But it could be that this time I charged the battery a few days earlier and took it with me. In this case, would it be wiser to put it back on the charger the night before (even though the LED says it is full)?

The reason the voltage drops there, is that you were climbing at full throttle.
That always puts a big load on the battery and it will recover after you ease up on the throttle.

Ah even in normal mode, not in speed mode and even to 3.2 V per cell? Thank you. I'm just surprised that I don't see any red cell voltages (3.2V etc) in older logs. I have to admit that I'm only looking at the logs only now and I have checkt only a few old logs and I don't have a good feel for them yet. That's why I'm happy if someone with more understanding about the logs tells me their opinion.

The red cell voltages in the DJI Flight Log Viewer make me nervous because many years ago I almost lost an Air 1 that suddenly dropped from 65% charge to 0% and made an emergency landing. The battery was ruined. The incident took the life out of the battery, so I was only able to hover for 1 minute with that battery.

But if you say that red voltages are normal when the throttle is pushed, then I am reassured.

It's not a temperature thing, it because you eased up on the throttle.

Thanks for the tip.

I think I'll look at the logs more often in future, and perhaps switch to the battery screen from time to time in flight to monitor the cell voltage in flight.

 

[Meta4]

many years ago I almost lost an Air 1 that suddenly dropped from 65% charge to 0% and made an emergency landing. The battery was ruined. The incident took the life out of the battery, so I was only able to hover for 1 minute with that battery.

If the battery showed 65% at the start of the flight, it had probably been discharging for days.
The % indicator is only accurate if the battery is fully charged at the start of the flight.
If it's showing 65% at the start, the cell voltages are going to be less than what they should be for a genuine 65%.

Ah even in normal mode, not in speed mode and even to 3.2 V per cell?....
But if you say that red voltages are normal when the throttle is pushed, then I am reassured.

It's normal for the cell voltages to drop when the drone is under load.
It's not normal to drop to 3.2 volts right at the start.
That yours did and the 93% indication at the start is a clue that the battery had discharged for some time and the 93% indication was not correct.

 

[dimizu]

If the battery showed 65% at the start of the flight, it had probably been discharging for days.
The % indicator is only accurate if the battery is fully charged at the start of the flight.
If it's showing 65% at the start, the cell voltages are going to be less than what they should be for a genuine 65%.

I didn't phrase it clearly. The battery was fully charged. It worked normally from 100% to 65%, then suddenly dropped from 65% to 0%. But this is an old topic that has long since been sorted out.

That yours did and the 93% indication at the start is a clue that the battery had discharged for some time and the 93% indication was not correct.

Yes, you are propapyl right.

It's normal for the cell voltages to drop when the drone is under load.
It's not normal to drop to 3.2 volts right at the start.

Thank you very much for your valutation. That calms me.

On the other hand, I have now uploaded the logs to Airdata and see under Power > Volts and Amps that I have low voltage warnings (darkest blue), which according to Airdata are to be assessed as follows:

Voltage placemarks (letters)
Placemarks (letters) represent the location where notable voltage drops occurred. Voltage drops are normal and typically happen along with higher current (Amp) use. It is normal to see voltage drops when the load of the aircraft increases (Amps), typically seen when climbing up.
The lighter blue voltage drops (0.05v-0.1v) are normal and are seen on many flights. The darker blue voltage drops (more than 0.1v) happen more rarely and should be inspected more closely. Last, the darkest blue color indicates that the voltage dropped below 10v, which may indicate a risky flight condition. The low voltage indicator will show up on approximately 7% of all flights.


If I believe aitdata, then I would probably have to throw away the battery.

 

[Meta4]

If I believe aitdata, then I would probably have to throw away the battery.

I don't think that Airdata is showing that the battery should be thrown out.
Any battery will show poorly if it is not fully charged when you start a flight.
Charge that battery to to 100%, do a test flight and come back with the flight data and we can see what the real state of the battery is.

 

[dimizu]

I don't think that Airdata is showing that the battery should be thrown out.

No, airdata doesn't say that, it was just a figure of speech. Airdata just says: "the darkest blue color indicates that the voltage dropped below 10v, which may indicate a risky flight condition"

Charge that battery to to 100%, do a test flight and come back with the flight data and we can see what the real state of the battery is.

Yes, that's what I'm going to do. For the next flights I will fully charge the battery the night before the flight and then have a look at the logs after the flight.

And I would also analyse more old logs (older than a year). I might find older flight starts at 98% to see what happened when the battery was younger.

I will also change the way I handle my batteries. I often recharged them fully after a flight, thinking they would discharge themselves anyway if I didn't fly in the next few days. Now, after some reading, I think it's better to only fly to 35% charge (Read in flight in the DJI Fly app) and then leave the batteries without recharging until the evening before the next flight. (35 % charge on flight musst be circa 2 leds and seams a good storage voltage)

 

[waynorth]

I think it's better to only fly to 35% charge (Read in flight in the DJI Fly app) and then leave the batteries without recharging until the evening before the next flight. (35 % charge on flight musst be circa 2 leds and seams a good storage voltage)

There is no problem flying until the battery has 10-15% charge left, it will not harm the battery.
Then charge it to approx 50-60% charge, this is called storage mode. It can be stored for 2-3 months in this state.
The day before you plan to fly again, you can fully charge the battery.
Never store a fully charged battery for more than 2-3 days.

 

[dimizu]

Never store a fully charged battery for more than 2-3 days.

Even if it is a smart battery that discharges on its own when not in use?

 

[waynorth]

Even if it is a smart battery that discharges on its own when not in use?

Yes. I consider the self-discharge function as an emergency function, to save the battery from damage.
There is no point in leaving the battery fully charged even if it discharges (very slowly). You have to charge it before a flight anyway, never fly with a battery that has been stored for more than 2 days. Always top up the charge before flying.
Also, never store a battery with very low charge, it will eventually discharge below a critical level and become a paper weight.
Batteries are expensive and a critical component, and I try to take care of them in the best possible way.

 

[dimizu]

Yes. I consider the self-discharge function as an emergency function, to save the battery from damage.
There is no point in leaving the battery fully charged even if it discharges (very slowly). You have to charge it before a flight anyway, never fly with a battery that has been stored for more than 2 days. Always top up the charge before flying.
Also, never store a battery with very low charge, it will eventually discharge below a critical level and become a paper weight.

Thank you very much. In future I will do exactly as you say.

 

[GrimtheViking]

Thank you very much. In future I will do exactly as you say

Try running 1 battery down to below 5%, just hovering in the garden and after cooling down charge fully back up again until it stops charging then turn the battery on whilst still in the charger and see if it will charge a bit more before it stops charging.. This may reset the battery. Then try a near monitored flight and see how you get on. Just a suggestion before dumping any of your batteries.