Battery wear level(usable capacity)

[sajindra]

Hii i have phantom 3 standard. I usually press and hold the power button 10 secs for check its lifetime. When I press it today 2 LEDs were flashing. One was blinking. It means my battery capacity is between 50-75%.but when I check it via Dji go app it mentioned 4180 mah usable. It means my battery wear level (usable capacity) is around 92.9% . (4500-4180 =320%45=7.1%. 100-7.1=92.9% usable. ). This doesn't make sense to me and I still get solid 20 minutes plus flying time. Any idea guys?

 

[Mark The Droner]

My understanding is that it is assumed the battery is good for 300 cycles. So when the battery is new, you will have four lamps. When the battery uses about 75 cycles, you'll have 3 lamps. And so on.

The mAh is different in that the max mAh is showing you how many "hours" (milliampere hours) the battery can run for on a full charge, and this number normally decreases as it ages.

 

[sajindra]

My understanding is that it is assumed the battery is good for 300 cycles. So when the battery is new, you will have four lamps. When the battery uses about 75 cycles, you'll have 3 lamps. And so on.

The mAh is different in that the max mAh is showing you how many "hours" (milliampere hours) the battery can run for on a full charge, and this number normally decreases as it ages.

I saw youtube video mentioned that, it's dangerous for using a battery with 3 LEDs. So what exactly these LEDs are showing?

 

[Mark The Droner]

It has to do what DJI believes is the "life" of the battery, which they say is 300 cycles. However, I've never known anybody who had a battery that lasted 300 cycles or even close. Personally, I ignore this so-called "life" because there are too many other things that are more important, in my opinion, such as cell balance, mAh, temperature, and swelling.

 

[Mark The Droner]

I saw youtube video mentioned that, it's dangerous for using a battery with 3 LEDs. So what exactly these LEDs are showing?

There are two different kinds of information available via the lamp indicators on the intelligent batteries.

The most common one that everybody knows is the "battery charge check." Simply press the button once and let go and it will show X number of lamps to indicate the current charge of the battery. Then the lamps will go off. You can also turn the battery on and it will show you exactly the same thing, except the lamps won't go off until you turn the battery off.

The second indicator is not as commonly known. I'm sure there are many people who are not even aware of its existence. And that is the "battery life check." And that is what I've been referring to. The battery life check is checked by pressing and holding the battery button for at least 5 seconds, then let go.

Neither of these has anything to do with mAh, which has to do with time, that is, how long will the battery stay on before it's depleted, or how long will your flight last before the battery is critical. The higher your max mAh, the more minutes you'll get out of a flight on a fully charged battery. This "max mAh" number starts or should start at or above the rated mAh printed on the battery when it was new, but unfortunately the max mAh will decrease as the battery ages. The mAh is one of the columns in the log. You can see where the number starts and watch it decrease during flight. The percentage of battery charge is calculated from this number.

 

[N017RW]

I saw youtube video mentioned that, it's dangerous for using a battery with 3 LEDs. So what exactly these LEDs are showing?

Don’t believe everything you see on YT, or anywhere, as truth.

 

[With The Birds]

There are two different kinds of information available via the lamp indicators on the intelligent batteries.

The most common one that everybody knows is the "battery charge check." Simply press the button once and let go and it will show X number of lamps to indicate the current charge of the battery. Then the lamps will go off. You can also turn the battery on and it will show you exactly the same thing, except the lamps won't go off until you turn the battery off.

The second indicator is not as commonly known. I'm sure there are many people who are not even aware of its existence. And that is the "battery life check." And that is what I've been referring to. The battery life check is checked by pressing and holding the battery button for at least 5 seconds, then let go.

Neither of these has anything to do with mAh, which has to do with time, that is, how long will the battery stay on before it's depleted, or how long will your flight last before the battery is critical. The higher your max mAh, the more minutes you'll get out of a flight on a fully charged battery. This "max mAh" number starts or should start at or above the rated mAh printed on the battery when it was new, but unfortunately the max mAh will decrease as the battery ages. The mAh is one of the columns in the log. You can see where the number starts and watch it decrease during flight. The percentage of battery charge is calculated from this number.

The means of remaining capacity determination you are referencing (simple coulomb counting) is commonly employed in many applications. The current DJI batteries employ a more advanced system which includes impedence tracking (IR determined during charge, discharge (average & peak load) and relaxed state for cells individually to provide for 99% demonstrated accuracy for the service life of the pack. Simple coulomb counting can be 50% out as a pack ages.

The total mah avaialable from a pack can be misleading, total usable capacity is limited to the weakest cell. The Texas Instruments Battery management SOC allows for this and includes IR in the battery life reporting (total mah capacity can be misleading absent performance under load in actual usage).

Prior to smart batteries I had lipos that the charger reported were at or close to manufacturer quoted Mah ratings that hit LVC within a fraction of the expected flight time.

 

[solentlife]

DJI used to state 200 cycles as the expected life .... each cycle based on a full charge / discharge. But DJI advised that they removed the automatic stop of the battery at 200 and its possible for battery to continue on. As to whether true or not remains to be seen.
Claims of accuracy of charge display and cycle life are innacurate at best.
I was in correspondence with DJI specifically on this matter way back as their advisorys were unclear ... depending on which Service Centre replied / person - replies were different !

Many people misunderstand the cycle / life part - thinking that each time they plug in charger - means 1 more cycle. Not correct. Each plug in is a partial increment of a cycle.
This means that its easy for a user to have 400 - 500 plug ins or more to make up the 200 full cycles.

Nigel

 

[solentlife]

This matter of capacity - is also one of the most misunderstood matters of batterys - especially when it comes to LiPo's ....

As WtB says ... a battery can show full of the charger - but deliver much less .. why ? Internal Resistance. As the battery is used time and again ... the iR increases, this creates a voltage drop. As iR increases - the voltage drop increases. This is seen in the shorter flight times of older batterys. Eventually the iR gets to a level that you find battery is substantially less for flight ... then its only good for bench use and low power demands.

With DJI batterys - the ONLY way to determine condition is by flying ... which given the efforts of DJI to create a battery for idiots ... is somewhat strange ! The reason is that DJI do not allow you access to the cells to directly measure iR and voltage independently.
Actually there is another way to check the battery but involves using a discharger and timer .... the discharger must be capable of reasonably high amps to force iR to to create the voltage droip seen in flight. The discharger to display voltage and you time it to a set low voltage state from full ... 15.4V as its nominal.

Nigel

 

[With The Birds]

This matter of capacity - is also one of the most misunderstood matters of batterys - especially when it comes to LiPo's ....

As WtB says ... a battery can show full of the charger - but deliver much less .. why ? Internal Resistance. As the battery is used time and again ... the iR increases, this creates a voltage drop. As iR increases - the voltage drop increases. This is seen in the shorter flight times of older batterys. Eventually the iR gets to a level that you find battery is substantially less for flight ... then its only good for bench use and low power demands.

With DJI batterys - the ONLY way to determine condition is by flying ... which given the efforts of DJI to create a battery for idiots ... is somewhat strange ! The reason is that DJI do not allow you access to the cells to directly measure iR and voltage independently.
Actually there is another way to check the battery but involves using a discharger and timer .... the discharger must be capable of reasonably high amps to force iR to to create the voltage droip seen in flight. The discharger to display voltage and you time it to a set low voltage state from full ... 15.4V as its nominal.

Nigel

These batteries do a better job of measuring cell parameters than most might ever hope to- why go to the trouble of load testing when IR (independently for each cell) is measured under actual flight load conditions and factored into the “fuel gauge” and time to empty algorithms. Texas Instruments cals this “impedance track”. Actually the cells are constantly evaluated during charging, flight and rest states to ensure the total usable & available capacity, time to empty and real time level are reported with 99% accuracy. I would like convenient access to the cell taps also however even better would be serial port access so you could run the DJI battery software to see all parameters, including IR.

 

[solentlife]

Myself and a number of electronics guys I fly all sorts with have looked at dismantled DJI batterys looking for causes and also to get idea of what goes on under the plastic case ...

What we found does not agree with perceived 'intelligence' .... we found cells not reported correctly ... unbalanced cells .... iR all over the shop ....

Sorry but the DJI battery does a good job of approximating what an experienced LiPo user can do - but that's it. Its designed for the lowest denominator of buyers of DJI ... those that have no idea how to manage LiPo cells ... to claim otherwise is IMHO overstating ...

Nigel

 

[With The Birds]

Myself and a number of electronics guys I fly all sorts with have looked at dismantled DJI batterys looking for causes and also to get idea of what goes on under the plastic case ...

What we found does not agree with perceived 'intelligence' .... we found cells not reported correctly ... unbalanced cells .... iR all over the shop ....

Sorry but the DJI battery does a good job of approximating what an experienced LiPo user can do - but that's it. Its designed for the lowest denominator of buyers of DJI ... those that have no idea how to manage LiPo cells ... to claim otherwise is IMHO overstating ...

Nigel

It’s what’s happening at the software level in the battery that reveals more than any examination of the board components might. if you have time please read this brief explanation of the monitoring functions and algorithms employed in the P3 & 4 batteries http://www.ti.com/lit/an/slua364b/slua364b.pd. It’s difficult to imagine how even the most experienced user with lab grade instruments might do a a better job.

 

[solentlife]

Does not change the facts of what myself and a number of others have observed.

One comment. Measurement of Internal Resistance is fraught with errors depending on how and where its done. Because it is subject to the tiniest influence of any wire or component in the path ... it is recognised fact that valid is only when measured direct at the cell itself. I have dedicated IR meters as well as IR measurement on chargers - I know how to do it by volts / amps / time manually .... and they all give different results !
The only advantage of the Ti board is that it makes the measurements reportedly at same charge levels and same physical location via the board. Therefore it is a reference form that uses CHANGE of results ...

This is a subject that will never be agreed across various ...

Nigel

 

[With The Birds]

Does not change the facts of what myself and a number of others have observed.

One comment. Measurement of Internal Resistance is fraught with errors depending on how and where its done. Because it is subject to the tiniest influence of any wire or component in the path ... it is recognised fact that valid is only when measured direct at the cell itself. I have dedicated IR meters as well as IR measurement on chargers - I know how to do it by volts / amps / time manually .... and they all give different results !
The only advantage of the Ti board is that it makes the measurements reportedly at same charge levels and same physical location via the board. Therefore it is a reference form that uses CHANGE of results ...

This is a subject that will never be agreed across various ...

Nigel

We don’t need to agree, I think of this more as increasing understanding. I like to know how things work. I have more confidence in the TI algorithm in my batteries than any assurance I might gain with any test Instruments.

impedence track measures IR at full capacity and at about 11% down and then every 3.3% increment is depletion while in actual use flying (all IR measurements are normalised to 0deg C also). These measurements are constantly compared to stored values so the capacity, time to empty and % remaining reported is with 99% accuracy for the full service life of the packs.

I think we can disregard and resistance value if the centre tap oigtails, they are factored in when the cells are first profiled when new so any effect is accounted for.