Looking for Mini 3 rapid charger that can charge 3+ batteries at once

[Droning on and on...]

Most DJI batteries charge about 1C give or take, I've thrown 100W at my Mavic 2 batteries (3850mAh @ 17.6v) and they barely even got warm.

This really doesn't make sense. You can't force ("throw") power at a load. All you can do is apply a voltage, and the load will draw the current it's gonna draw.

A load can't tell the power rating of a voltage at it's input. A passive 10 ohm resistor will draw 1A from a 10V supply, whether that supply has a 25W or 10kW capacity.

An active load actually controls current draw, electronically, to meet whatever the operational requirements of the load are. In the case of DJI batteries, that will be whatever is necessary for a 1C lipo charge profile.

YOU CAN'T FORCE MORE CURRENT INTO THE BATTERY WITH A HIGHER POWER CAPACITY CHARGER. That's not how electronics works.

So this discussion is academic... There's nothing informative here, regarding charge rates and currents, that is useful in any way, at all, for managing charging DJI Intelligent Battery modules, any DJI drone prior to the USB-C minis.

Now, the Minis brought Power Delivery into the picture which gives the LOAD more flexibility in knowing supply capability and more finely controlling charge voltage. This is what makes different charging rates possible, but the key here is PD not the supply power capacity. It's PD that makes higher charge/current rates possible, supply allowing.

 

[Droning on and on...]

I think that a better, simpler, cheaper solution is to just buy more batteries.

I would recommend also getting the DJI serial multicharger, and simply develop the habit of charging batteries the night/morning before a flight. With USB-C PD, just plug in to a powerbank, throw it all in bag, and grab it on your way out.

I used to buy parallel chargers for every model. I found that the times I actually, truly, NEEDED that ability was, well, never. Usually after flying 3 batteries I'm done.

 

[MaximusCZ]

Since Mini 3 pro (even the fly more combo) doesnt come with wall brick, I am using my Apple charger. Interestingly, when charging battery in drone it draws more than 30 Watts (33, 35 iirc?), but the same powerbrick connected to the fly-more craddle holding 3 batteries only charges at 18 Watts max.

Clearly the drone charging circuitry is negotiating differently than the 3-battery craddle, and I have no idea why. Its also entirely possible that with more standart wall-brick the craddle would charge also at 30+ watts, as my experience shows that some devices capable of negotiating 30w charging fail with this apple brick and fall down to 5w instead, while sucking 30w happily from another brick.

Has anyone succesfully charged a battery in a fly-more-craddle with 30+ watts? If so, what charger are u using?

 

[CanadaDrone]

I would recommend also getting the DJI serial multicharger, and simply develop the habit of charging batteries the night/morning before a flight. With USB-C PD, just plug in to a powerbank, throw it all in bag, and grab it on your way out.

I used to buy parallel chargers for every model. I found that the times I actually, truly, NEEDED that ability was, well, never. Usually after flying 3 batteries I'm done.

I think the reason most people bought the aftermarket chargers was because they do two very important things DJI chargers do not:

1) They can discharge the batteries
2) They can apply a balanced storage charge

The parallel charging is just a bonus haha.

The M3P hub lets you use it as a battery bank for discharging, which is better than nothing, but I suspect it doesn't discharge all 3 batteries evenly when in battery bank mode so you would need to put one battery in at a time to discharge to storage level (which you will have to estimate, and won't be balanced). I can't find one in stock yet to test myself though.

When Hanatora gets their M3P charger out that will probably be the one to get. They are inexpensive and full featured compared to DJI's versions. I have their M2P version and the only downside is the charging brick it comes with - not very portable.

 

[kingsnake11]

While I understand everything you're saying above, it's completely irrelevant to DJI batteries. You have no control over the current the battery assembly draws. That is controlled by the internal BMS.

While perhaps an interesting academic discussion, it has no bearing on anything you can control.

unless you are going to use a 3rd party charger....I have no idea as to how the BMS controls that. I do know that third party chargers will speed up charging times for batteries for spark, air, and mavic pro 1 and 2.... . Nonetheless, charging at 1C is still the best practice for battery longevity. Sorry to have bored you with the info...but understanding Lipo's is ingrained in those of us who also fly RC systems other than quadcopters...which is what these DJI aerial systems are.

 

[Droning on and on...]

unless you are going to use a 3rd party charger....I have no idea as to how the BMS controls that.

It doesn't.

The BMS has no idea what's presenting a voltage. It simply starts trying to charge the battery if the voltage is sufficient.

The only way the charger can affect BMS behavior is by being underpowered – unable to meet the current load the BMS is trying to draw, which results in the supply voltage dropping, and then depending on the smarts of the BMS it will either adjust its load and just charge more slowly (keeping the charge voltage up and stable), or, refuse to charge altogether.

People make the mistake of thinking DJI smart batteries are like simple lipo packs, where the charger connects directly to the cells themselves, so you can do things like measure cell voltage to determine state-of-charge.

This is completely wrong. Especially so with DJI Intelligent Batteries. When you turn the battery on, the voltage at the terminals is the output of a power FET on the BMS, not the direct output of the lipo cells.

Was everyone here aware that when a battery is fully charged, it's not the charger that shuts off charging but the battery?

 

[moldorf]

I'm having a hard time understanding how any lithium battery with a BMS will have any significant reduction in life by being regularly charged at an average of 25 watts rather than 10 watts. I understand the temperature gradients but from everything I've seen DJI batteries have a much higher operating temperature than charging temperature. By that I mean when I remove a battery from the drone immediately after a flight it's always much warmer than when I remove a battery from the charger immediately after a fast charge

what am I missing?

 

[Droning on and on...]

Calling the controller in DJI Intelligent Batteries a "BMS" is a bit of lazy shorthand. It is much much more than a BMS.

In practice the only thing you can really do to protect a DJI Intelligent Battery is to avoid full-charge to storage charge through automatic discharge. The 100% charge stresses lipo cells, so avoid fully charging when you don't know for certain you're going to fly.

That's it. All this other nonsense about discharging parallel chargers, managing charge state through voltage levels, etc., while correct for naked lipo packs, amounts to no more than a whole lot of Battery Virtue Signalling when it comes to DJI Intelligent Batteries.

 

[MaximusCZ]

I'm having a hard time understanding how any lithium battery with a BMS will have any significant reduction in life by being regularly charged at an average of 25 watts rather than 10 watts

The BMS is not some magic chip that makes batteries last longer and charge faster at the same time.

The appeal of fast charging is big these years, and not many people realize it is shortening their battery life a lot. The BMS is programmed to balance charging speed with longetivity. Could batteries charge 20% faster than they do now? Sure, but battery longetivity would take a hit that DJI is not willing to take. Could batteries charge 20% slower than they do now? Sure, you can do so by connecting it to lower-wattage rated charger, and the batteries will last longer.

Charging 10 or 25 watts can be a big difference, depending on the capacity of the cell. The regular Mini 3 pro Battery has 18.1 Wh of storage, so we are talking of charging by 0.55 or 1.38 C rate.

It has been tested countless times that higher charging rate is worse for battery capacity retention as you cycle it. This, along with temperature and "final state of charge" (ie charging to 100%? 90%? of max), are major determinants of how much charge will a battery hold as it gains charge cycles.

For maximum battery longetivity, you want slow charging (0.1 - 0.5C) at low temperatures (20°C, 68°F), and ideally to stop charging at around 80%, and never discharge under 20%.

Of course, we cant always meet those conditions (and charging to only 80% goes directly against our interest), but its worth avoiding fast charging anytime you can, and not charging batteries to 100% if you know you wont be flying today. Its keep them at 80% and charge to 100% as close in time to discharging them as you possibly can.

 

[MaximusCZ]

Figure 3: Cycle performance of Li-ion with 1C, 2C and 3C charge and discharge (link)

@moldorf Even tho your post was deleted (I pressume because it was VERY long), It still landed in my email inbox.
I agree that saying "higher charge current will degrade your battery quicker" without supporting it with data was not ideal. When I was writing post above I googled for a graph to illustrate my point, but got plenty irrelevant results and gave up. But now you made me google again and I finally found some graphs illustrating my point. Of course we cant control discharge rate, which sits between 2 and 3 C for normal battery (20-30 mins of flight time), but we can control charge rate at least.

You cited a lot of results from pages highly optimized to rank high in google results, most stating that fast charging doesnt damage the battery because it charges fast at first, switching to slow charging later. This is not reserved for fast chargers. As long as I remember (and maybe from the very first Li-ion/Li-po cells in wide production), the chargers first charge with fix current (meaning the voltage is set dynamically), and near the end it switches to fixed voltage, allowing current to reduce as cell is finishing charging. Its true the closer you charge towards 100% the more damaging it is to battery, and is where most damage comes from. But that doesnt mean that increasing current in the first half of charge cycle has 0 effect on the battery health.

How far (or how fully) you charge your battery reflects on its health like this:

Figure 5: Effects on cycle life at elevated charge voltages [2] (link)
Higher charge voltages boost capacity but lowers cycle life and compromises safety.

 

[moldorf]

View attachment 153327
Figure 3: Cycle performance of Li-ion with 1C, 2C and 3C charge and discharge (link)

@moldorf Even tho your post was deleted (I pressume because it was VERY long), It still landed in my email inbox.
I agree that saying "higher charge current will degrade your battery quicker" without supporting it with data was not ideal. When I was writing post above I googled for a graph to illustrate my point, but got plenty irrelevant results and gave up. But now you made me google again and I finally found some graphs illustrating my point. Of course we cant control discharge rate, which sits between 2 and 3 C for normal battery (20-30 mins of flight time), but we can control charge rate at least.

You cited a lot of results from pages highly optimized to rank high in google results, most stating that fast charging doesnt damage the battery because it charges fast at first, switching to slow charging later. This is not reserved for fast chargers. As long as I remember (and maybe from the very first Li-ion/Li-po cells in wide production), the chargers first charge with fix current (meaning the voltage is set dynamically), and near the end it switches to fixed voltage, allowing current to reduce as cell is finishing charging. Its true the closer you charge towards 100% the more damaging it is to battery, and is where most damage comes from. But that doesnt mean that increasing current in the first half of charge cycle has 0 effect on the battery health.

How far (or how fully) you charge your battery reflects on its health like this:
View attachment 153328
Figure 5: Effects on cycle life at elevated charge voltages [2] (link)
Higher charge voltages boost capacity but lowers cycle life and compromises safety.

it was too long a post. But I think the main reason I deleted it was that the links were essentially vague declarations, and I did ask for some numbers rather than assertions

my take on your earlier post was that there is likely some degradation of the battery from fast charging. But the level of that 'damage' was probably secondary to the damage from charging that last 10-20% of a battery bringing it up to 100% charge (which you talked about). That at least I was familiar with because of all the years I've been charging deep cycle batteries in my RV's. In those cases, the smart charging management systems tended to maintain charging up to 85-90% of capacity. They would not allow "topping off" the charge, which on a 12 volt system would actually be in the 14.4-14.8V range. The cutoff was usually in the 13.2V range, and any use would quickly drop the current to 12.8V (this is for an AGM system)

as I mentioned, when I'm around home is I recharge my drone batteries it will usually be in the 5V/2amp/10watt range. But if I'm out and about on my regular camping trips, I'll be using fast-charging, and again, that fast charging rate probably won't be more than 60-65% of the max charge of the batteries.

My hunch is that kind of personal protocol won't significantly shorten the life of the batteries. If perfect charging conditions yield 600 charging cycles, and my occasional hasty charging yields 450 charging cycles, I won't notice because that would be a failing battery 4-5 years from now. I can also mitigate the damage by paying up-front for an extra couple of batteries. That will spread the occasional fast charging over more batteries

(by the way, the link you provided was based upon data from 2002 and 2016. I'd wonder if the newer protocols, methods, and technology has altered the data significantly. Further, that data was for Li-on batteries while the M3 Pro batteries are Li-po)

 

[Droning on and on...]

For maximum battery longetivity, you want slow charging (0.1 - 0.5C) at low temperatures (20°C, 68°F), and ideally to stop charging at around 80%, and never discharge under 20%.

Of course, we cant always meet those conditions (and charging to only 80% goes directly against our interest), but its worth avoiding fast charging anytime you can, and not charging batteries to 100% if you know you wont be flying today. Its keep them at 80% and charge to 100% as close in time to discharging them as you possibly can.

"We" can't access the cell voltages directly, so there is nothing meaningful we can do to noticeably affect life and performance.

Here's one to consider: When the intelligent BMS indicates 100% charge, what does that mean? Measuring the voltage at the connector simply give the voltage the BMS is producing at it's out FET.

Let's say instead it was a reliable direct measure of the cell voltage. It reads (equivalent) 4.2V per cell. Do we conclude this a full charge, every electron possible that the cell will accept has been shoved in there, so if we don't discharge soon damage will occur?

Or, did engineers at DJI design the whole system to cut short during the CV phase of the charge cycle, at say 90% total capacity, and call it 100%?

Does anyone know? DJI engineers aren't fools. Were I designing a battery module for this application, I sure would design in all sorts of safety margins.

Does anyone know?

While much of the discussion here is correct, we can only apply it to naked lipos where we can directly measure the state of charge, and directly control the charging process at the cell contacts with and external power supply and balancer.

The DJI Intelligent battery is a black box.

@MaximusCZ, when a DJI battery indicates full charge, are the lipo cells at full charge? 95%? 90%? Do you know?

 

[Droning on and on...]

Simply put, the charge rate a battery can accept safely is a matter of design.

Lipos and more traditional li-ion cylindrical cells are available that can charge at 10C reliably and without compromising cycle life significantly. They're very expensive. None of us are willing to spend $1,000 on a drone battery just so we can charge it in 6 minutes. Oh, and it takes a special, expensive charger.

OTOH, for an application like an electric car, the cost premium makes sense to pay.

 

[MaximusCZ]

"We" can't access the cell voltages directly, so there is nothing meaningful we can do to noticeably affect life and performance.

For sure we cant access direct cell voltage, but honestly we dont need to. Charging slower is all we can do, and it helps. It probably wont double you battery life, but hell, it might. I think 20-30% longer life is safe bet.

And while we cant access cell voltages directly, when plugged in turned on drone, the drone actually reports cell voltage to the app (where you can see it in battery info). Tho I remember reading a comment about BMS actually reporting single voltage of the 2s battery, and its just the app dividing it by two and showing it as real values. I have no idea about how much truth is in this, but makes one wonder. (iirc it was discussing mini 2 batteries, might have changed with mini 3)

Do we conclude this a full charge, every electron possible that the cell will accept has been shoved in there, so if we don't discharge soon damage will occur?

The cell is not a bottle with a clear brim that serves as the upper limit of how much water it can hold. Better analogy would be a sponge. There is theoretical limit of how much energy a cell can store, but given that each cell is physically different and every cell is not 100% perfect (every atom at its supposed position), the actual limit is lower. But even approaching this therotical maximum would destroy any cell before that maximum would even be reached. The physical maximum is lower, but that doesnt mean you want to approach even this physical maximum..

Damage happens even during regular use. Even if you are charging super slowly from 50 to 51%, the battery is suffering irreversible damage. The thing is, during some states, the damage a battery is suffering is much, much, much lower than during other states. If you only use the middle 50% of the battery (25-75% range), you can get multiple times more cycles (even when we count two 25->75% charges as one cycle) from the cell, compared to cell being cycled from 0% to 100%.

The closer you approach cell limit, the exponentially more damage the cell is sustaining. The 100% charge state is human selected voltage level (physical properties of a cell are taken into account) that the cells get charged to. You could charge the cell to the higher voltage levels, and it would hold more energy, but would degrade way faster. You could charge it less, and it would last longer. Selected 100% voltage is a tradeoff between longterm battery longetivity and light-time of each flight. Everybody wants as long flight times as possible, so DJI is incentivized to squeeze as much from the batteries as possible. Using the 100% of what these batteries are programmed to give us is already on the very punishing end for the batteries, its best to never use the battery to 0% not only from the standpoint of loosing the drone. On the other side of the charge limit, stopping charging at 80% would help prolong the battery longetivity trendemously, but lets be honest, who of us would bother to vigilantly watch over batteries on charger to unplug them prematurely and then loose another 5+ minutes of flight time. I certainly dont, I understand and accept that the batteries are being pushed to the limits, and probably wont last much longer than 300 cycles. And thats okay. But when the matter of choice between slow and fast charging is just using less powerfull wall adapter (if Im not in a hurry to charge asap to fly right away), it can only help the battery last longer.

I am not saying everyone is doing it wrong, I am not saying everyone is stupid for doing it the other way, and I am not persuading anyone to change their charging habbits. All I am doing is laying down facts about battery tech, how treating the battery affects its performance over its lifetime, and thus allowing people to make more informed decisions on how they want to treat their batteries.

@MaximusCZ, when a DJI battery indicates full charge, are the lipo cells at full charge? 95%? 90%? Do you know?

To adress this speciffically: There is no true 100%. Its a choice (that DJI is making for us) of where to draw a line and saying "stop charging beyond this point, its not worth it". You can check the second graph at the end of this post of mine to see that charging charging the battery to 4.35V per cell yields more energy stored (line starts higher) than charging to 4.25V, but is damaging the battery to the degree where in less than 100 cycles, the maximum charge a battery can hold drops below what a battery charged to 4.25V would hold.

 

[Robert Prior]

I understand and accept that the batteries are being pushed to the limits, and probably wont last much longer than 300 cycles.

Long enough for my purposes, given that I haven't made 100 flights with any of my batteries yet. I'm more worried about bricking the battery of my least-used drone by forgetting to keep it charged.

 

[moldorf]

Long enough for my purposes, given that I haven't made 100 flights with any of my batteries yet. I'm more worried about bricking the battery of my least-used drone by forgetting to keep it charged.

yeah....I have both a Mini 2 & a Mini 3. I use them about equally...maybe a little more with the Mini 3. I have 5 batteries for the Mini2 and 7 for the Mini 3. I rotate the use of the batteries, and on average I probably fly 2-3 days a week, less in winter; and one or two flights on flying days. And probably, on average, 0.67-0.75 charge cycles per flight

in other words, I'm looking at a maximum of 300-400 charging cycles a year distributed over a dozen batteries. And the reality is, at minimum, I will fast charge, maybe, about half that time. Meaning that IF (I'm still not convinced it's true to any significant level) fast charging at 50-60% of a battery's max rate actually shortens the life of a battery....I will never notice

 

[Droning on and on...]

For sure we cant access direct cell voltage, but honestly we dont need to. Charging slower is all we can do, and it helps. It probably wont double you battery life, but hell, it might. I think 20-30% longer life is safe bet.

Based on what? Speculation?

Do you know something about these modules you haven't shared? The type/brand of lipo cell being used, for example?

If not, then your speculation is as good as mine, and I say everything your discussing here was considered in the design of the Intelligent Battery controller, there is already margin built in at the top and bottom of charge state, storage discharge, etc.

I assert that actively managing the charge state will not result in any meaningful, perhaps not even measurable difference in capacity, or cycle life over letting the battery manage itself.

Reason is the Intelligent Battery is already doing that, with many years of refinement in the engineering and design.

All you're doing is fighting it, maybe even defeating it.

I think we've both made thorough cases here for our respective opinions, so I'm going to bow out now. Readers are definitely more informed and better able to make their own choice based a lot of good information we have both provided.

Safe and fun flying!