IF...I am correct about this, I do NOT believe that the DJI app will indicate the power level of the batteries in the Range Extender...UNLESS you are running a P2V+. If you have a P2v, you WILL see the icon, but I don't think it will ever change to show a charge....
And...I agree with the posts here...the Extender is very slow to recharge...usually taking several times longer than the main P2V battery. When I first got my P2V, I charged it for several hours...with not a glimmer of green...finally I went to bed and woke up the next morning to a Green LIGHT...wheeeee...!
I'm also not sure that an Apple wall-wart will provide adequate charging current. I think if you are using an Apple wall-wart that is furnished with the iPad, you are on solid ground as it is rated at 2.1 Amps. The iPad needs a huskier current to charge it than an iPhone, iTouch, etc. Those smaller devices are just fine with a 1 Amp charger. The charger that I got with my P2V is rated at 2 Amps as well, however the initial charge from a 'dead' battery DOES take a very long time...
Here is a link to my more extensive thoughts and experience about all of this...
viewtopic.php?f=4&t=13254&start=30#p121804
Keep in mind that not all USB ports are the same...for starters some are not even powered, but meant to only provide a way to connect a USB device's signal lines to a PC, etc. Others DO have the power lines activated...and USB power will always be the correct VOLTAGE...that being 5 volts. However...and here is where a lot of people get lost...there can be a HUGE difference in the "Amp Rating"...this being the measurement of the "AMOUNT OF CURRENT" that is available to charge any device. It's important here to understand that using a higher current (i.e. Amp) rating of your charger will NOT damage...or overload...or burn out...a device that is attached to it. For further reading....see the link I have posted above...
Hope this helps...If not, I've wasted 50 years of working in electronics....!!