Best battery discharge method?

[msinger]

What seems to catch a lot of people out is that the auto landing will initiate when the % set for “critical low battery” is reached. You can’t set it below 10% so I think we might safely say they autoland will commence at 10% as the absolute min %.

That's a common misconception. When the set critically low battery level is reached, DJI GO displays a message to alert the pilot. The drone does not use that DJI GO setting.

 

[Former Member]

All this being said, people, dont deliberately plan to fly your battery down to 10% or even 15% unless you are aware of the consequences and risks. Not worth it to me. I plan to land at 20-25%.

 

[WithTheBirds]

That's a common misconception. When the set critically low battery level is reached, DJI GO displays a message to alert the pilot. The drone does not use that DJI GO setting.

So your confident you might be able to fly around at 9% without autoland commencing? I havent been able to unless I’m flat stick on the throttle to stop the descent with any of my phantoms. I haven’t tested on the M2, I don’t plan to by choice either.

 

[Former Member]

Do any members here drive their car "beyond the E slash?"

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[Garritynet]

It is a throwback to the battery software.

The software controls the maximum and minimum charge on the battery. If a lipo battery ever truly goes to 0% or very close, it will be difficult to ever charge it again. There are also obvious problems if it overcharges. So the software controls minimum and maximum charges. It also needs to know the batteries state in between these amounts. Two things to keep in mind... the battery really goes by voltage per cell and converts this to a percentage and the software needs to know the max and min charges but also where it is in between. A battery might be drained down to 30% and charged back up to 80%, drained to 50% and charged back to 95%. Under the old software is was possible that the the software would not know the correct lower and upper charge of the battery. Or at least DJI thought this might be an issue. Since that time, things have changed.

However, I can't think of any real harm this would cause. Perhaps for some people this caused a problem so DJI simply stop recommending it.

Maybe they just got tired of all the emails from people like me asking the same question and they figured it would be cheaper to replace a few drones than to pay someone to answer them all.

 

[msinger]

So your confident you might be able to fly around at 9% without autoland commencing?

I have not tried that. I'm not sure it's possible.

I'm only confident that the critically low battery setting in DJI GO is not used by the drone (as you suggested it was).

 

[WithTheBirds]

I have not tried that. I'm not sure it's possible.

I'm only confident that the critically low battery setting in DJI GO is not used by the drone (as you suggested it was).

Im hoping your right- suspecting now you may be.

Having had the opportunity to look in the Mavic 2 manual it says that auto land (critical) will be initiated at 5% with no opportunity to override. This is really good news for obvious reasons. Less of our newer entrants to the hobby needing to watch their shiny new toy landing 20m in front of them over water or in similarly unfortunate scenarios.

While there may have been updates I know for a fact the P3 would try and commence an auto-land at the set critical level percentage. This seemed really stupid given obviously it could be set at a high level in GO and I am sure it brought a lot of people unstuck. I managed to simulate this with two different batteries and only one occasion was deliberate. Silly me for setting it to 20%.

 

[WithTheBirds]

All this being said, people, dont deliberately plan to fly your battery down to 10% or even 15% unless you are aware of the consequences and risks. Not worth it to me. I plan to land at 20-25%.

Another benefit of landing around 20%- if I plan to fly within the coming week I can leave the batteries to charge just before I plan to fly (no need to bring them up to storage charge level). A hobbit that follows me from managing dumb LiPO's.

 

[Former Member]

Having had the opportunity to look in the Mavic 2 manual it says that auto land (critical) will be initiated at 5% with no opportunity to override.

Excellent. (M2 manual P44)

https://dl.djicdn.com/downloads/Mavic_2/20180827/Mavic 2 Pro Zoom User Manual_v1.0.pdf

 

[msinger]

Having had the opportunity to look in the Mavic 2 manual it says that auto land (critical) will be initiated at 5% with no opportunity to override

The Mavic 2's critically low battery level is not hard coded to 5%. The drone will land when it decides it only has enough battery power left to safely make it to the ground.

I know for a fact the P3 would try and commence an auto-land at the set critical level percentage

No P3 models try to auto land at the critically low setting in DJI GO.

 

[WithTheBirds]

It is a throwback to the battery software.

The software controls the maximum and minimum charge on the battery. If a lipo battery ever truly goes to 0% or very close, it will be difficult to ever charge it again. There are also obvious problems if it overcharges. So the software controls minimum and maximum charges. It also needs to know the batteries state in between these amounts. Two things to keep in mind... the battery really goes by voltage per cell and converts this to a percentage and the software needs to know the max and min charges but also where it is in between. A battery might be drained down to 30% and charged back up to 80%, drained to 50% and charged back to 95%. Under the old software is was possible that the the software would not know the correct lower and upper charge of the battery. Or at least DJI thought this might be an issue. Since that time, things have changed.

However, I can't think of any real harm this would cause. Perhaps for some people this caused a problem so DJI simply stop recommending it.

And here lies the most probable explanation to the mystery for the original deep discharge recommendation from DJI.

Earlier batteries almost certainly employed either/and table based voltage measurement or coulomb counting. You have mentioned the voltage based system where if a particular LiPO is carefully measured in an actual application plotting voltage against determined capacity can build a fairly accurate table which can be used to inform the remaining % gauge. Also often employed is simple coulomb counting where Ah delivered to the load in use is subtracted from the expected battery capacity.

While these now outdated methods can be pretty good they aren't without problems. They certainly can't allow for changes in temperature, discharge rate, the age of the cells or how the battery has been treated (depth of discharge, storage level, time at full charge, temperature etc).

The GAS gauging and impedance tracking algorithms we have in our current DJI packs take cell condition (internal resistance), temp, actual load etc into account in determining the state of charge %. While the earlier employed methods will perform a self calibration of sorts by being discharged to a low level it is unnecessary with the currently employed battery management systems.

The harm that might be caused in performing the deep discharge is wasting charge cycles that could be used flying and unduly stressing the pack.

 

[WithTheBirds]

The Mavic 2's critically low battery level is not hard coded to 5%. The drone will land when it decides it only has enough battery power left to safely make it to the ground.


No P3 models try to auto land at the critically low setting in DJI GO.

As I said earlier- mine did. Perhaps this was altered in later software/firmware. Btw- I am not alone in this observation, there are two other P3 owners I am aware of who noted the same performance.

Btw- I am unsure why you might be so adamant about the 5% figure in the absence of any direct experience- DJI manual states that critical battery level alert at less than 5% cannot be cancelled (above 5% it can be).

 

[msinger]

Btw- I am unsure why you might be so adamant about the 5% figure in the absence of any direct experience- DJI manual states that critical battery level alert at less than 5% cannot be cancelled (above 5% it can be).

I'm not sure what that means. I own a Mavic 2 Pro and am just clearing up any confusion so others don't think they can fly to 10% (or it now seems you're saying 5%) before the drone will auto land.

 

[WithTheBirds]

I'm not sure what that means. I own a Mavic 2 Pro and am just clearing up any confusion so others don't think they can fly to 10% (or it now seems you're saying 5%) before the drone will auto land.

I’m not sure either. I’m prepared to accept the M2 won’t alutoland at the user defined setting in go, I haven’t tried it and am not aware of actual confirmation from those with real world performance. The manual does say that the critical warning can be overridden by the operator at levels above 5% but not at or below 5%. Unless the manual is wrong that means to fly below 5% battery would require applying throttle to halt descent with no opportunity to increase altitude.

 

[mbsz53]

Thank you for that. That error should really be pointed out to DJI, because the battery wont allow itself to be self-discharged to 0, and you cant fly it down to 0. The low voltage sensor in the battery and drone will force itself to land when battery level gets to 8%. Thats why many drones end up as fish bait after landing in the water, with the owner trying to return home in an unanticipated headwind.

DJI should point out that fully discharging a lipo is different than discharging it to 0. If a lipo ever gets to 0, it is officially dead, if it hasnt exploded or swelled first. Not joking. Sometimes if a lipo gets below 2.8v in any cell, it has been irreparably damaged.

Im glad you found that in the manual. There are a few other things in the manual that are ambiguous, and you have to guess what DJI means and come to your own conclusion.

You mentioned swelling. I was discharging my batteries to 0% for the second time (twentieth cycle) and now they are swelling to the point of disconnecting in flight. Can you please expound on this?

 

[mbsz53]

I'm not sure what that means. I own a Mavic 2 Pro and am just clearing up any confusion so others don't think they can fly to 10% (or it now seems you're saying 5%) before the drone will auto land.

Can the batteries be drained to 0% sitting on the ground?

 

[msinger]

Can the batteries be drained to 0% sitting on the ground?

No. They will auto shut off before they are completely depleted.

 

[mbsz53]

Just let it sit. As mentioned it will discharge down to the correct storage voltage. You don't need to discharge them down to a 0% reading at any time.

That's not what the manual says.

 

[Former Member]

You mentioned swelling. I was discharging my batteries to 0% for the second time (twentieth cycle) and now they are swelling to the point of disconnecting in flight. Can you please expound on this?

You have to be careful with that. If they have already swollen, they might also not latch in properly, and can pop out during flight. Plus, they are no longer stable, and all kinds of bad things could happen.

If it were me, as soon as a battery swells, I never use it for flight again.

 

[WithTheBirds]

Can the batteries be drained to 0% sitting on the ground?

The batteries can be drained to the point where the low voltage cut-out has been set in the battery firmware. In the interests of protecting the cells from permanent damage this will be at some point above 3V. Some have reported 3.3V as the setting. I don't know what it is for the Mavic. If you leave a LiPO sitting long enough it will self discharge to the point where it is permanently damaged beyond being usable. Most agree now that the deep discharge routine is of no real benefit. If I think about my battery failures over the years with LiPO's puffed cells have almost always followed deep discharge (usually pushing my luck with the flight time but also forgetting to check a pack in storage). As has been said- swollen packs should be considered dead, they can't be trusted. I would be careful where I left it sitting also, there is a slim chance it could burst with spectacular results. None of mine ever have however the cells are definitely less stable than they might be in a healthy pack.