Battery reporting false percentage left

[shockwave199]

I never ran into this one yet. I charged up my battery, which was so low from sitting a while that I had to turn it on to charge. All was fine and it charged without issue. Popped it in the bird and a couple hours later when I powered up everything to fly, just before I took off I looked at the battery percentage and it was at 73%. That was alarming. Within a minute it dropped to 70% and I hadn't even taken off. The cells showed a full charge though. It just wasn't squaring up and making sense. Since it wasn't a big deal to not fly the location (company bbq) I powered down and didn't fly what was to be a litchi mission. But I was in the dji app when this happened. I just figured my battery was shot and that was that, or maybe I somehow had the darn thing on without realizing it the whole time (not so though). Later in the day I wanted to fly down whatever was left on the battery and in the absence of a crowd around now, assess what's going on. But this time the battery showed 98% and all was well. I flew the battery down with a perfectly normal flight to 49% and landed at that for a decent storage charge.

Why the false reporting? Anyone run into that one? Kinda sorry I didn't restart everything initially but weird quirks like that put me off from flying, especially a nonessential flight.

 

[RedHotPoker]

Are you deep cycling them intelligent flight batteries?
I know, some may say they don't, but it may help.
Drain down to 8% and fully charge, after every ten full charges.
This us supposed to help. Does it? Time will tell.

RedHotPoker

 

[shockwave199]

Since the battery was so low it wouldn't start charging unless I turned it on, I'm assuming it was at a very low percentage that could possibly be equivalent of deep cycle. Not sure though. And I'm not sure that's it because it reported correctly later on.

 

[RedHotPoker]

Letting a regular LiPo battery drain that low, can often damage it.
Hopefully that hasn't happened here. Even though you weren't flying for a time, and the batteries do go into an auto discharge, it's best to check on them regularly... I don't like to rely on a single button press, instead place them in the drone, and see what the Go app battery page reads.
I have my fingers crossed that @dji will bring back Battery Life in the iOS app version. ;-)

RedHotPoker

 

[flyNfrank]

I would also check it in the flight log file and see what was reported at that point.

 

[Mocho]

Had a similar issue last week. Inadvertently ran the battery down to 4%.
It charged fine, showed 100% when I took off but within a minute of flying showed 48% so I just landed and recharged it.
Everything seems fine with that battery now, I chalked it up to confusing the smart system by running it down so low. I often run my batteries down to 8% with this firmware vr. and have not had that issue?

 

[SnoozeDoggyDog]

Are you deep cycling them intelligent flight batteries?
I know, some may say they don't, but it may help.
Drain down to 8% and fully charge, after every ten full charges.
This us supposed to help. Does it? Time will tell.

RedHotPoker

What he said!

 

[shockwave199]

I believe it's 20 cycles until deep discharge, not 10. I'm not into doing that, frankly. Some are, some aren't. I'm not. I'm gonna write this off as an odd glitch, since the situation corrected itself on restart and the battery performed fine. I know which battery it is though and I'll be keeping an eye on it.

 

[Digdat0]

I believe it's 20 cycles until deep discharge, not 10. I'm not into doing that, frankly. Some are, some aren't. I'm not. I'm gonna write this off as an odd glitch, since the situation corrected itself on restart and the battery performed fine. I know which battery it is though and I'll be keeping an eye on it.

You should post up the flight log on phantom help, I'm curious what the VoLTS looked like when it dropped. If the voltage dropped too, could indicate a bigger issue. But, based on what you noted probably just an odd glitch and a one off.

 

[ROD PAINTER]

It was probably in hibernation!


Sent from my iPhone using PhantomPilots

 

[tcope]

First, no one should be only flying and looking at the percentage only. You should also turn on and be looking at the voltage (lowest cell) while you fly.

The percentage is a _guess_... it's based on the voltage at the time, how fast the battery is voltage is dropping over a period of time, etc. If something is not a constant, that percentage is going to be incorrect. Having the battery drop to a critical storage level and than having to turn it on to change is probably going to throw that percentage algorythm off. This is why DJI recommend a deep discharge every 10 cycles (used to be 20). 8% is really the lowest the battery should be. But keep in mind, it's really the voltage level when the battery is at "8%"... I'm just using 8% as this is what DJI states. So now when you charge it back up to 100% the battery firmware knows what a full charge on _that_ battery is. As batteries age, that "100%" changes. That is, it's top charge can change and it's discharge rate can change. This can even change based on the temp outside.

Go into settings and turn on the voltage display while you are flying.
Take your batteries down to 8% every 10 cycles. To those that don't and only watch the percentage... you may not see a problem but I also wish you luck.

IMHO, msigner made one of the best posts ever on battery levels. I'd recommend reading it, reading it again and perhaps even printing it and taking it into the field:

HOW TO: Monitor battery voltage to watch for signs of failure

 

[shockwave199]

I monitored the volts too. Like I said initially, even when I had the glitch the volts were showing full per cell. That's what was weird but with the percentage dropping I didn't trust anything at that point. I've always had the voltage showing with percentage too. Later, all performed normally. I'm gonna toss it up to an app glitch, but I'll keep an eye on it.

 

[RedHotPoker]

I believe it's 20 cycles until deep discharge, not 10. I'm not into doing that, frankly. Some are, some aren't. I'm not. I'm gonna write this off as an odd glitch, since the situation corrected itself on restart and the battery performed fine. I know which battery it is though and I'll be keeping an eye on it.

It was 20 full charges, they are recommending it be done after every ten now... ;-)

RedHotPoker

 

[Mocho]

It was 20 full charges, they are recommending it be done after every ten now... ;-)

RedHotPoker

I still believe the issue has to do with the battery running down below 8% as tcope implies.
In my opinion it is important to cycle them especially if your only running them down to 25+ % on a regular basis as it seems to me the smart system would need a FULL cycle in order to calibrate itself.

I'm used to deep cycling my LiPo's from my Buggy Racing day's. My Hyperion charger would indicate when the battery capacity (percentage remaining in DJI Go) would start dropping. Usually one or two cell's would start to be slightly offset and I would set my charger up to cycle the battery. This usually fixed it, and depending how much I dropped the voltage that race might mean a couple of cycles to get the cell voltages even and capacity back up . One thing we don't get to see is the batteries internal resistance which creeps up slowly with time and is a good indicator of the internal status of all the batteries cells.

 

[flyNfrank]

First, no one should be only flying and looking at the percentage only. You should also turn on and be looking at the voltage (lowest cell) while you fly.

The percentage is a _guess_... it's based on the voltage at the time, how fast the battery is voltage is dropping over a period of time, etc. If something is not a constant, that percentage is going to be incorrect. Having the battery drop to a critical storage level and than having to turn it on to change is probably going to throw that percentage algorythm off. This is why DJI recommend a deep discharge every 10 cycles (used to be 20). 8% is really the lowest the battery should be. But keep in mind, it's really the voltage level when the battery is at "8%"... I'm just using 8% as this is what DJI states. So now when you charge it back up to 100% the battery firmware knows what a full charge on _that_ battery is. As batteries age, that "100%" changes. That is, it's top charge can change and it's discharge rate can change. This can even change based on the temp outside.

Go into settings and turn on the voltage display while you are flying.
Take your batteries down to 8% every 10 cycles. To those that don't and only watch the percentage... you may not see a problem but I also wish you luck.

IMHO, msigner made one of the best posts ever on battery levels. I'd recommend reading it, reading it again and perhaps even printing it and taking it into the field:

HOW TO: Monitor battery voltage to watch for signs of failure

Nicely said!

 

[mcrazyhorse]

I still believe the issue has to do with the battery running down below 8% as tcope implies.
In my opinion it is important to cycle them especially if your only running them down to 25+ % on a regular basis as it seems to me the smart system would need a FULL cycle in order to calibrate itself.

I'm used to deep cycling my LiPo's from my Buggy Racing day's. My Hyperion charger would indicate when the battery capacity (percentage remaining in DJI Go) would start dropping. Usually one or two cell's would start to be slightly offset and I would set my charger up to cycle the battery. This usually fixed it, and depending how much I dropped the voltage that race might mean a couple of cycles to get the cell voltages even and capacity back up . One thing we don't get to see is the batteries internal resistance which creeps up slowly with time and is a good indicator of the internal status of all the batteries cells.

Agree about the resistance, but with the increase of resistance the voltage drop will increase so the per cell voltage charge will happen faster. Each battery has 4 cells. I think this is why they recommend a deep cycle charge every 10 or 20 charges to adjust the voltage per cell and equalize the voltage. The voltage is just a indication the real value of concern should be current. Current is calculated by dividing voltage by resistance therefore as the resistance increases the current decreases.

 

[shockwave199]

I've been flying my three batteries for a year and a half without being precious about it. I typically fly my batteries down to anywhere between 30-50%. I've never deep discharged although I have had batteries seemingly drop low enough during storage to have to turn them on to get them to charge. If anything I'm gonna be more diligent about checking them in storage and if needed charge them up to 50% if they've been sitting in storage for prolonged periods. My usual routine is to bring two batteries for critical shoots so there's always a backup in case of problems. I'll keep this glitch in mind and reboot the system if it happens again to see if it clears as it did this time. I've been fortunate that the occasional glitches haven't been catastrophic. Let's hope that continues!

 

[Vertigo]

Agree about the resistance, but with the increase of resistance the voltage drop will increase so the per cell voltage charge will happen faster. Each battery has 4 cells. I think this is why they recommend a deep cycle charge every 10 or 20 charges to adjust the voltage per cell and equalize the voltage. The voltage is just a indication the real value of concern should be current.

A few things; first of all, voltage is not just an indication, its THE indication of charge level. But it needs context. Voltage drops as load increases (voltage sag), and temperature, battery condition and other factors will influence the relationship between voltage and capacity.

Secondly, balancing is not the same as deep cycling. Balancing cells is done every time you charge your battery. Deep cycling is pointless for a lipo battery from a chemical POV, but it does help the not-so intelligent battery to gauge battery condition to make its % estimate more accurate. Thats the only reason I can think of that it makes any sense, to recalibrate the charge/discharge curve to accommodate capacity loss. If your battery is in optimum condition, it shouldnt need this.