Today got a strange issue.... my P3A starts landing with 19% of battery left. In go app the Critical warning option was set to minimum 10%
Why? Fortunately I was near home.

I believe the DJI app calculates the needed power to return home safely with regard to altitude, distance, etc. Idk how far/ not far away the P3 was from the home point but that probably had something to do with it. And you want to be returning home under 20% battery anyways. Better safe than sorry

shayanza@usc.ed Posted at 2016-6-15 16:50
I believe the DJI app calculates the needed power to return home safely with regard to altitude, dis ...

You're right, better back home with 20% or more. But Dji  should change this behavior  otherwise it makes non sense the option for critical low power.

Did you get any warnings?  Did you start flying with a battery at less than fully charged?  Normally it'll do this if it reaches a critical voltage regardless of the percentage left.  I've had it with a partially-charged cold battery at around 50% when pushing it hard.

nigelw Posted at 2016-6-15 18:40
Did you get any warnings?  Did you start flying with a battery at less than fully charged?  Normally ...

None of these. take off with 97% and warning "Critical low battery. Landing" when I'm coming to home point and was 700 meters away. Battery level was 19% and my set for this option is 10%.
Yesterday I updated my P3A with las fw 1.9.60.  May a fw related problem???

This is the link of the flight

http://healthydrones.com/main?share=dxMyvA

Blowin' free Posted at 2016-6-15 17:57
None of these. take off with 97% and warning "Critical low battery. Landing" when I'm coming to ho ...

Not sure.  It does get quite hot at 53°C but I wouldn't expect that to be a problem.  There's certainly nothing about critical voltages.  Have you checked your settings in the app to see if it's meant to RTH on low battery or whatever?

nigelw Posted at 2016-6-16 00:40
Did you get any warnings?  Did you start flying with a battery at less than fully charged?  Normally ...

Correct, in the cold and pushing it hard will make the cells drop.
Just make sure you are on the latest firmware.

Blowin' free Posted at 2016-6-16 00:57
None of these. take off with 97% and warning "Critical low battery. Landing" when I'm coming to ho ...

Above post refers to why.
As good practice you should be close by when the battery gets low.

Blowin' free Posted at 2016-6-16 00:57
None of these. take off with 97% and warning "Critical low battery. Landing" when I'm coming to ho ...

The battery voltage may have drawn down to the critical level as the phantom was returning home.
Looks like you flew very far, almost 3km and lost radio connection.  With a moderate wind its possible your phantom will not make it back before the battery dies.  You were lucky this time.

nigelw Posted at 2016-6-15 19:10
Not sure.  It does get quite hot at 53°C but I wouldn't expect that to be a problem.  There's cer ...

Settings are ok. I think it's a software hidden behavior that overlaps the Critical low battery setting in the go app.
Otherwiswe I expect that a battery level of 10% is sufficient to Landing anywhere the Aircraft is, so don't understand why it happened at 19% level

Blowin' free Posted at 2016-6-15 10:36
Settings are ok. I think it's a software hidden behavior that overlaps the Critical low battery se ...

What was the wind like? Altitude shows 1073.1 ft, so it may have been windy. Looks like you were decreasing altitude at the time?  I've experienced, in low battery states (<30% remaining), if you fly into hard wind (20mph+) or increase/decrease altitude at 100% throttle when the batteries are already hot (40+ degree C), it will pull more volts on the battery and will hit a critical state and auto landing kicks in. Cell voltage can drop, despite the overall volts being 'okay' to fly. I remove the last 10% from my flight time and pretend I only have 90% of battery to fly. I try and land way before that .. meaning, I wouldn't be at 1000 feet up with only 19% battery remaining. Plus, the last 30% goes faster than the first 30% IMO.

digdat0 Posted at 2016-6-15 19:14
What was the wind like? Altitude shows 1073.1 ft, so it may have been windy. Looks like you were de ...

But is is slightly confusing.
If the setting is 10%, then that's what it should land at. Not 19%.

richmars Posted at 2016-6-15 11:20
But is is slightly confusing.
If the setting is 10%, then that's what it should land at. Not 19%.

I believe its a fail safe built in where the batteries get over heated and the cell volts are too low to keep going much further. I think its independent of the overall battery charge state and is designed to prevent unexpected crashes. Yes, 10% should be it .. but if the hardware/software detects an issue way before that, you would prefer it to tell you and start to auto-land, rather than keep going unnoticed and have an unexpected crash?

digdat0 Posted at 2016-6-15 19:29
I believe its a fail safe built in where the batteries get over heated and the cell volts are too  ...

This is a classic case of potentially sacrificing the aircraft to save the battery though.  If the power drops quickly you'd expect the software/battery meter to reflect it, or at the very least flash an alarm saying land now or die.  It should never land unexpectedly without control in any circumstances.  You could be only 50 meters away but over a 400ft drop into a forest below for example, where the aircraft would be destroyed & potentially unreachable.  I often fly from the top of mountains where auto landing would mean a very difficult descent on foot to retrieve an almost certainly damaged P3.

nigelw Posted at 2016-6-16 02:51
This is a classic case of potentially sacrificing the aircraft to save the battery though.  If the ...

While the drone may start to descend, you can push up on the left stick and still gain altitude. I have had some situations when I was told the battery was critically low between 10 and 20 per cent.

First of all, you should be on your way home at 35 to 40 per cent. I use 40 per cent and if you have a strong headwind, use 50%. That of course means that by the time you hit 20 per cent you should be pretty close to home. If you find your craft descending, push up on the control stick to maintain altitude and push the right stick all the way in whatever direction you need to get home. You can increase speed in Atti mode and use less battery drain but that will not be of much advantage if you have a strong cross wind and you need to be able to use Atti mode well. Otherwise, just use GPS mode, keep the altitude as high as you can and keep it coming towards you. At least if you run out of power it should not be far away.

skipilot1 Posted at 2016-6-15 12:05
While the drone may start to descend, you can push up on the left stick and still gain altitude. I ...

You can do this, but power will eventually cut out and the phantom will fall from the sky. It happened to me 2 days ago.

digdat0 Posted at 2016-6-16 03:59
You can do this, but power will eventually cut out and the phantom will fall from the sky. It happ ...

I have tested the quad after coming home at a football field with about 15 per cent power and about 50 meters height. I was able to fly the length off the field and keep the quad in the sky until it was at 7 per cent. Perhaps my time will come, but I blame myself for bad planning if I get back to the home point with less than 25 per cent and that is with the quad at 60 meters height.

I appreciate the warnings about low battery, high and cold temperatures.  However, this happened to me only a few days ago for the first time after 700,000 feet flown and 80+ hours.  I took off with 68% battery, ~18C, climbed to 200 feet, and got the critically low voltage, landing warning. Absolutely ridiculous.  Was able to steer slightly away from a populated field, but toppled it beside a sidewalk. This happened just before the last firmware update.  If you look at the number of views, this topic is getting a lot of hits lately.

I have had that happen. Although the battery was around 12% As suggested above I feel that the current is being checked or your Phantoms calculating the time in the air and making a judgement call as to how much power is required to RTH.

rodger Posted at 2016-6-16 11:00
I have had that happen. Although the battery was around 12% As suggested above I feel that the curre ...

Yes, but in this case it was not intending to return home, it decided to land where it was, and at that point it was 700 Metres from home. But you are right in that the aircraft is checking on available power all the time, and it unfortunately does not necessarily agree with the bqattery capacity display. The display is a calculated amount, not an absolute value, and as such it can change during a flight.

What most likely happened is that the aircraft was monitoring your battery and decided that the remaining capacity was not sufficient to continue horizontal flight, and for the safety of the aircraft, the best course of action would be to land immediately while it has enough reserve power to land safely. Sadly it does not know what terrain it is over at that time, could be water.

hbax450 Posted at 2016-6-16 08:28
I appreciate the warnings about low battery, high and cold temperatures.  However, this happened to  ...

You are supposed to take off with the battery at 100% or close. It is in the manual.

hbax450 Posted at 2016-6-16 01:28
I appreciate the warnings about low battery, high and cold temperatures.  However, this happened to  ...

A cold battery at 68% will have a good voltage on the ground, but as soon as it's pushed (by ascending) the voltage will drop quickly because the battery is too cold for the chemical reaction to take place at a fast enough rate.  If you start with a fully charged battery, by the time it gets to 68% it's much warmer & working at full capacity.  It's not a fault.