There might be more than 2 terminals to the batteries, since there are 3
batteries and their voltages are displayed.

Opening the module without damage is easy, with a small vice. Stick it in
there and squeeze, about 1 inch of the rear, about 1/8 inch deep to cover
along the cap portion. In other words... Grab about 1 inch worth of the cap
portion of the module (the back end), and squeeze. The back part of the cap
pops right off and you can use a tiny screwdriver to unclip the rest.

--

I wrote:

> I thought DJI was expensive, but Autel is almost twice the price for an
> entry-level drone. The less expensive drone makers use C.R.A.P. technology
> and other weirdness like not selling additional propellers and whatever
> other parts. Can't believe how cheap lesser brand controllers are compared
> to DJI. The phone holder on even $300 drones is a single plastic plunger
> with a simple spring inside the controller for tension! You can hear the
> spring creaking.
>
> DJI messed up the firmware or software for the Mini 2, so I'm waiting to
> get back into FPV flight with that one.
>
>
>
> https://www.ebay.com/itm/175008269834
>
> The seller accepted $300 for that old technology DJI Mavic Air (Arctic
> White).
>
> Additional batteries are OUTRAGEOUSLY expensive, at least twice the price
> of other DJI drone batteries.
>
> Can the provided battery shell be used as a connector for homemade
> batteries?
>
> Of course there are only 2 terminals to the actual battery inside of the
> shell, so they can be connected to whatever batteries that will work
> (Sanyo NCR2070C sourced enough current to work well in prior tests with
> another drone). Lipo is ideal, but that Sanyo "C" model sources lots of
> current.
>
> Besides measuring temperature, what other connectors might be related to
> the battery? I suppose any temperature sensor can be left hanging (with
> the appropriate caution).
>
> I suppose they could defeat battery mods by trying to communicate with the
> battery circuitry, but apparently not since there is AFAIK no mention of
> that by anybody who has tried connecting batteries to it.

*cells

I can get into the battery firmware using "DJI Battery Killer" (or similar)
and a hardware interface "CP2112" from my PC to the drone battery.

But not sure if using one battery management system (BMS) while swapping
batteries to that BMS is possible, at least not without adding two more
capacitors (or whatever stuff might be needed).

John Doe <always.look@message.header> wrote in
news:t3djc5$59t$5@dont-email.me:

> I can get into the battery firmware using "DJI Battery Killer" (or
> similar) and a hardware interface "CP2112" from my PC to the drone
> battery.
>
> But not sure if using one battery management system (BMS) while
> swapping batteries to that BMS is possible, at least not without
> adding two more capacitors (or whatever stuff might be needed).
>

My battery packs for my drone is ten inches long, three inches wide and
an inch and a half thick. My drone propellers are 10" in diameter.

DJI? Bwuahahahahah! OK... mine is similar... it is a drone. But
it is way bigger than a DJI.

It works! At least preliminarily. It requires 1 10 mF capacitor and 3 1/10
W resistors. The capacitor drains fast when the battery management system
is not in power failure mode (a bit disappointing, but no big surprise),
but not too fast. On a 3s Mavic Air BMS, after unplugging the battery, the
cap went down to 9.2 V before it was re-plugged. Still functioned. Maybe
it can get down to at least 9 V. In any case, that probably is enough time
to switch batteries, unless you fumble the operation.

That is for using only one BMS circuit board and switching batteries to
it, as opposed to using one BMS per battery. It might be advantageous with
only one BMS circuit board available. For a Mavic Air, the required 10 mF
cap is only 14 g, the 3 1/10 W resistors are weightless. The resistors are
used as a voltage divider so the BMS thinks the battery midpoints are
connected.

I wrote:

> I can get into the battery firmware using "DJI Battery Killer" (or
> similar) and a hardware interface "CP2112" from my PC to the drone
> battery.
>
> But not sure if using one battery management system (BMS) while swapping
> batteries to that BMS is possible, at least not without adding two more
> capacitors (or whatever stuff might be needed).

John Doe <always.look@message.header> wrote in
news:t3e55u$lkj$1@dont-email.me:

> It works! At least preliminarily. It requires 1 10 mF capacitor
> and 3 1/10 W resistors. The capacitor drains fast when the battery
> management system is not in power failure mode (a bit
> disappointing, but no big surprise), but not too fast. On a 3s
> Mavic Air BMS, after unplugging the battery, the cap went down to
> 9.2 V before it was re-plugged. Still functioned. Maybe it can get
> down to at least 9 V. In any case, that probably is enough time
> to switch batteries, unless you fumble the operation.
>
> That is for using only one BMS circuit board and switching
> batteries to it, as opposed to using one BMS per battery. It might
> be advantageous with only one BMS circuit board available. For a
> Mavic Air, the required 10 mF cap is only 14 g, the 3 1/10 W
> resistors are weightless. The resistors are used as a voltage
> divider so the BMS thinks the battery midpoints are connected.
>

> I wrote:
>
>> I can get into the battery firmware using "DJI Battery Killer"
>> (or similar) and a hardware interface "CP2112" from my PC to the
>> drone battery.
>>
>> But not sure if using one battery management system (BMS) while
>> swapping batteries to that BMS is possible, at least not without
>> adding two more capacitors (or whatever stuff might be needed).
>
>
Having "right to repair" issues with a lame manufacturer?

You should see what Taylor and McDonalds did to its franchises.

On a sunny day (Sat, 16 Apr 2022 10:18:38 -0000 (UTC)) it happened John Doe
<always.look@message.header> wrote in <t3e55u$lkj$1@dont-email.me>:

>It works! At least preliminarily. It requires 1 10 mF capacitor and 3 1/10

The 'm' stands for 'milli'
I take it you did mean 'uF' 'micro Farad'

For the ret I still have no idea what you are doing.
But my drone works.

Jan Panteltje wrote:

> John Doe wrote:
>
>> It works! At least preliminarily. It requires 1 10 mF capacitor and 3
>> 1/10
>
> The 'm' stands for 'milli'

Very good! At 14 g, a Rubycon PX 10 mF cap from Digi-Key seems to work.

Putting that cap across the V+ and V- terminals of the battery management
system seems to keep the BMS from dropping below its power failure mode
cutoff voltage (or doing any other mischief) when swapping batteries.

Usually a DJI drone user swaps batteries with each having an integrated
BMS circuit board, but this (preliminary) solution requires only one BMS.

Used 6.8 k resistors for a divider to the otherwise unconnected battery
midpoints. Maybe 10 k will work.

On a sunny day (Sat, 16 Apr 2022 17:35:25 -0000 (UTC)) it happened John Doe
<always.look@message.header> wrote in <t3euot$ej4$1@dont-email.me>:

>Jan Panteltje wrote:
>
>> John Doe wrote:
>>
>>> It works! At least preliminarily. It requires 1 10 mF capacitor and 3
>>> 1/10
>>
>> The 'm' stands for 'milli'
>
>Very good! At 14 g, a Rubycon PX 10 mF cap from Digi-Key seems to work.
>
>Putting that cap across the V+ and V- terminals of the battery management
>system seems to keep the BMS from dropping below its power failure mode
>cutoff voltage (or doing any other mischief) when swapping batteries.
>
>Usually a DJI drone user swaps batteries with each having an integrated
>BMS circuit board, but this (preliminary) solution requires only one BMS.
>
>Used 6.8 k resistors for a divider to the otherwise unconnected battery
>midpoints. Maybe 10 k will work.

OK, thanks, think I got it now :-)

The big capacitor discharges down to at least 8 V (to a BMS for a 3s
battery) before the circuit locks up. That's probably PLENTY of time to
swap batteries.

The reason is to convert DJI drones to use ordinary lipo batteries,
especially ABANDONED DJI drones with unbelievably high-priced batteries.

I suppose having 3 outputs, maybe 1" long each, from the battery
management system won't hurt anything since it's ground and two digital
signal lines. I suppose capacitance might be a factor but I don't know how
long of a wire has an effect on that on the given circuit (or even
generally).

Those wires are for resetting the BMS in case the capacitor does discharge
too far. The reset is a simple process. Apparently completely discharging
the capacitor is required, maybe to reboot the BMS before reseting it.

Not sure I'll use it, but looks like a possibility. Apparently they
corrected FPV mode on the Mini 2 (they temporarily messed it up). So now
it probably is a better FPV experience than the Mavic Air (1).

Learning how to coordinate movements with the joystick. STEEP learning
curve.

I wrote:

> It works! At least preliminarily. It requires 1 10 mF capacitor and 3
> 1/10 W resistors. The capacitor drains fast when the battery management
> system is not in power failure mode (a bit disappointing, but no big
> surprise), but not too fast. On a 3s Mavic Air BMS, after unplugging the
> battery, the cap went down to 9.2 V before it was re-plugged. Still
> functioned. Maybe it can get down to at least 9 V. In any case, that
> probably is enough time to switch batteries, unless you fumble the
> operation.
>
> That is for using only one BMS circuit board and switching batteries to
> it, as opposed to using one BMS per battery. It might be advantageous
> with only one BMS circuit board available. For a Mavic Air, the required
> 10 mF cap is only 14 g, the 3 1/10 W resistors are weightless. The
> resistors are used as a voltage divider so the BMS thinks the battery
> midpoints are connected.
>
>
>
>
>
>
>
> I wrote:
>
>> I can get into the battery firmware using "DJI Battery Killer" (or
>> similar) and a hardware interface "CP2112" from my PC to the drone
>> battery.
>>
>> But not sure if using one battery management system (BMS) while
>> swapping batteries to that BMS is possible, at least not without adding
>> two more capacitors (or whatever stuff might be needed).
>