Is is possible to stop the RC Controller from charging the phone as well ?  It is draining the battery which then, making the 2nd drone battery meaningless.

The current is too small to charge your phone. Please do not worry about it.

If you are using a USB cable attached to the 2nd port (i.e. not the port on the side) it will charge the phone. If you use the port on the side of the controller it will not charge the phone.
I was using an HTC M8, which does not work with the side port, as the orieentation of the port on the phone is wrong, so I had to use the secondary USB port on the controller. This was charging my phone.
Have since picked up a dedicated phone to use (which has the port situated correctly for mavic use) and using the side port does not charge the phone.

Most smartphones have an option to turn off charging while connected to an USB-Accessory. Maybe this will help to solve your problem.

My RC is charging my phone too but I can empty 3 Mavic Batteries and still have around 15-20% power left in my RC.

I'm wondering how many mavic batteries can you go through before the RC is too low, on phones that the RC "doesn't" charge the batteries? Folks are saying it's minimal, it doesn't seem minimal to me on my droid maxx. After one mavic battery, my RC will be down to 75%.  

I've ordered a cable from Amazon (micro usb/micro usb) .. I'm going to do what I've heard others doing which is cutting the small black wire inside the cable... supposedly that stops the charging action..

jimmybbq Posted at 2017-6-2 06:16
I'm wondering how many mavic batteries can you go through before the RC is too low, on phones that the RC "doesn't" charge the batteries? Folks are saying it's minimal, it doesn't seem minimal to me on my droid maxx. After one mavic battery, my RC will be down to 75%.  

I've ordered a cable from Amazon (micro usb/micro usb) .. I'm going to do what I've heard others doing which is cutting the small black wire inside the cable... supposedly that stops the charging action..

I'm wondering how many mavic batteries can you go through before the RC is too low, on phones that the RC "doesn't" charge

I'm using iOS (not Android) so my mobile device doesn't get charged by my Mavic's remote, and I can usually go through 8-10 batteries on a fully-charged remote before it gets down to the dreaded 15%.

DJI Mindy Posted at 2017-5-4 01:29
The current is too small to charge your phone. Please do not worry about it.

... why does the phone tell you that it is charging?  By using the phone you drain more power than the RC can supply to charge the phones battery...

The phone does drain your RC battery... simple fix is to use an USB Powerbank, connect powerbank to RC and phone to other USB  connector... Now the powerbank charges the RC and the RC "charges" your phone...

patman89 Posted at 2017-5-4 06:34
Most smartphones have an option to turn off charging while connected to an USB-Accessory. Maybe this will help to solve your problem.

My RC is charging my phone too but I can empty 3 Mavic Batteries and still have around 15-20% power left in my RC.

Try 3 batteries just using the RC without the phone then see how much RC battery you have left. I bet it's over 50%. Just think how much flying you could do then.

I use SONY ZX Premium. After connecting the cable to side USB port, a pop-up screen will ask you four options. 1. Charge this device (phone)  2. Supply power (charge RC)  3. Transfer files 4. Use device as MIDI.
I select option 3 and think it will use a small current. However, I found that the battery symbol changed to "charging'.   I think I need to try the one suggest by DebG

app Disable Battery Charging ROOT

After extensive use, over 900 Km of flights, I found this is of little concern.  So just don't worry about.  Trust me.