As I understand the problem can not be solved at software level by dji, because the only app that allow to stop charging requires root level! So there is only one solution at this time is hardware, but the controller are already existing. As someone else explain in another thread it should modify the connexion. I haven't found on internet a cable that stop charging. There are only cable that stop data ?.
As some told me here, may be it is not a big deal to fly 3 batteries.
On ios is it a parameter in the dji app?