Bought 2 used phantom 2 batteries today. Each has 10 flights on it. All cells even. Flying in Canada it was -11 Celsius today.
Flight with battery 1 at 31% ph2 started flashing red and went into auto landing
Flight with battery 2 at 37% same thing happened.
I then checked all the cells again everything looks good. They both have square contacts so it's a new stock.
Can this happen due to cold weather?
When I landed, lights flashing green again and I was able take off again, so it only happened under load.

Yes, that is a cold weather issue.  Put your batteries in your pants to keep them warm.

LOL Jamie, "is that a huge ass quad battery in your pants, or are you just glad to see me?"

I do keep the batteries warm until the time I fly. But if it's a cold weather issue why is the lights green when it lands? If the battery was draining due to cold weather, the lights would remain flashing red when the quad lands

In simple terms, low temperature can cause the voltage to drop lower under load than it normally does, and kick in the low battery notification.  As the load is decreased the voltage rises, hence the absence of the alarm when the Phantom was at rest.  The batteries are not as efficient at temperatures near or below freezing.

I see...I talked a friend of mine and he tells me he flies temp -17 to -27 Celsius with no issues, go figure

tang2007 Posted at 2015-2-9 10:27
I see...I talked a friend of mine and he tells me he flies temp -17 to -27 Celsius with no issues, g ...

Bear in mind the OP was flying it down to 31% to 37%.  At rest the battery is probably down from 12.6 volts to around 11.6 to 11.7 volts.  Under load it was probably reading around 11.2 to 11.3 or less, and hitting the low battery threshold.

LiPo batteries store well at freezing or below, but don't operate as efficiently at those temps.

I hope these guys are wearing gloves.  My fingers get cold here in Florida when it's in the low 50's (F).

What I don't understand how is it triggering "critical low voltage" since it was showing me 37% on my screen? The phantom would land only if battery level drops to 15%, correct?

i thought you set the critical battery level in the assistant software (and i thought the default was like 30% or 35%), no?  if so, 37% is close enough *particularly in cold conditions* to trigger a rth i would think with fluctuations in the actual reading with temps/loads/etc.

tang2007 Posted at 2015-2-9 12:15
What I don't understand how is it triggering "critical low voltage" since it was showing me 37% on m ...

Hi, I think now, the phantom calculates how far away from home point it is and based on remaining battery level, will decide to RTH. This is actually very good if you are high and a fair distance off. It would require a lot more power than say , if 30 yds away and 10yds high.
Cheers!
Rod

I don't use low battery rth option and I dont reccomend it

tang2007 Posted at 2015-2-9 13:27
I don't use low battery rth option and I dont reccomend it

Hi Tang, why don't you recommend it?  have you had a bad experience with it?
I consider myself fairly experienced with the phantom but I leave it set permanently and have had no adverse happenings  yet on the times it has triggered...

Cheers!
Rod

I fly mostly fpv and i like to be in control

tang2007 Posted at 2015-2-9 14:03
I fly mostly fpv and i like to be in control

Oh I see. So a personal choice rather than a problematic area . Thanks for explaining your motivation- I did wonder whether you had a bad experience with it- if so it would have been good to share with us.
Cheers!
Rod.

tang2007 Posted at 2015-2-9 12:15
What I don't understand how is it triggering "critical low voltage" since it was showing me 37% on m ...

The battery capasity and voltage are not linear related,and the discharge curves are differert at different terperatures.
At low temperature,the capasity is 37%,but the voltage could be low as well.
And duiring flying ,the aircraft is under load,the current is high, therefor the voltage drop is significant.
After landing ,the current is low ,so the voltage could come up  ,is a normal phenomemon.
THX