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Why can't I increase the autonomy of my Tello?

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Feb 9, 2023
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I modified a Tello to accept the Mavic Air cell (LiPoHV, 2375mAh - 9,1Wh - 37gr) using the original Tello battery board.

I used an old (but still good) cell and got a runtime of about 8 minutes. Few.

So I bought some new cells (also to repair my Mavic Air batteries) and mounted one.
The maximum duration was 14 minutes, I can't go beyond that.

The weight of the "modified" drone is 90grams.

So I took another Tello with its original battery, ballasted it up to 90 grams (propeller guards and an additional 3g weight) and saw that it lasted 11 minutes.

The weight is the same, but the Mavic's cell is MUCH bigger (and better) than the Tello's.
At the same weight (important) I expected a duration of at least 20 minutes, but it wasn't like this.

So I used a microcomputer to recharge the (empty) 5V batteries via the Tello's USB port (5V energy monitor)

With the original battery the Tello use an energy of 3.9Wh (the Tello battery is 4.18Wh, it's OK) while with the Mavic battery the Tello use an energy of 5.6Wh (But the Mavic cell is 9.1Wh!).

Therefore the Mavic cell is not fully discharged, but only partially. And it is "strangely" equal to the Tello's maximum autonomy with a new battery.

In my opinion the Tello's BMS (in the battery or in the aircraft) operates in such a way that the maximum duration is always 13-14 minutes.

That's why I once asked what could happen by connecting the cell directly to the Tello's 4-pin connector...
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Looks like the Mavic Air cells are not rated for the current / C-rate, that Tello draws from it. It propably has a higher internal resistance and as a result, the voltage you get on the terminals reaches the lower limit much earlier just because of the higher voltage drop.

I guess, the Mavic Air cell get's pretty hot, when you use it this way...
Are you serious?
A 2375mAh battery in a Mavic Air will be drain in 15minutes.
This means that the Maivc batteries provide 9.6A only for stand by in hovering (30% power)!

Mavic Air battery, when I take it out, it's 64-65°C
The Mavic Air cell in the Tello it's letterally fresh when Tello tells me that it's over.

I managed Li-Po batteries since 2003, I've several charger and discharger.
I've continued discharge the Mavic cell at 5A: I've found the other 3Wh until reach 3.5V.

The proof?
Tell tells me that the Mavic cell it's over and blinks red light?
Just power off, remove, reconnect the cell and power on again. Here other 30% of battery, green light...
And I can fly other 4 minutes until 10%.

Ryze/DJI don't allow to fly over 13 minutes: it's locked.
OK, as you know better, why do you ask here and affront me?

By reading your story: As far as I remember, someone tested to fly Tello tethered and although it was provided with "unlimited" energy (with constant voltage) over wires, the battery indicator still was going down and flight time was limited. So it seems to be limited by firmware.
I'vent ask you anything, but you don't know the difference between a toy lipo cell and a Mavic Air cell, as you supposed, going against me immediately.

Thanks for your support.
The title of this thread contains a questionmark, so you asked a question.
I am working with all kinds LiPos and LiIon cells since 2014 and also build custom packs and create custom BMS hardware/software, so I guess I know about difference between those kind of cells.

Your statement, that Mavic Air drains it's battery within 15 minutes is not correct (as long as you fly the Mavic Air without additional payload).

Although Tello looks like a toy compared to Mavic Air, the battery is quite high sophisticated. It is a HV cell as well (can be charged to 4.3V) and is rated for high currents. That's the reason why until now no one found a replacement for that battery in that form factor, that performs better.

But the question why you cannot exceed 13-14 minutes seems to be answered anyway.
so I guess I know about difference between those kind of cells.

I don't think so, because you've told me that a brand new Mavic Air cell was worst than Tello or that a Mavic Air MUST have a payload to drain in 15 minutes (believing in 21 minutes DJI "fantasy story").

For you the answer was obvious, not the firmware issue.
I have proved that it is a firmware problem, not battery fault.

My question remains: what if I connect the cell directly to the Tello?

Anyway, maybe I remind you of someone who hit you as a child?
What's your problem? Relax, man... relax.
I have a Mavic Air as well and can confirm that 21 minutes are not a "fantasy story". If your Mavic Air battery reaches 64-65°C after 15 minutes there seems to be something severely wrong.

Your question "what if I connect the cell directly to the Tello?" does not remain, because it was not asked before.

But as you seem to be "Mr. Know-it-all-better", why don't you answer it by yourself? If you had taken a closer look to the "BMS" board of the battery, you would have seen that it is quite primitive and has no intelligence. That's why I am talking about the Tello firmware.

The question about things that may have gone wrong in someone's childhood is misplaced here, but should be mirrored back to you if your second post in this forum already starts with "Are you serious?"

Nevertheless, you should take a look here: Battery mod project for Tello
If you are capable of German language, you could also take a look here: Ryze Tello Akku parallel oder Alternative - Drohnen-Forum.de - Quadrocopter, Multicopter und FPV
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I have proved that it is a firmware problem, not battery fault.

Hm, you sure?

Did you used very short and very thick wires to connect the MA cells?

If you've eliminated voltage drop on wires as the cause, then the issue must really be in the BMS.
Note that for Tello, the battery board doesn't have one - well, depends what you define as BMS; there seem to only be undervoltage disable switch on the battery board. And temp sensor, but its output goes directly to main board.

Anyway, the programmable part of BMS (or bluntly, battery charger chip) in on the main board. You can check its documentation to figure out whether it can be programmed to assume specific pack capacity. If yes, then that probably can be altered using SBS protocol. There are tools to send commands through that.
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