I changed both key batteries on a porsche cayenne . Now I can not lock or unlock the car using the key. I also can not manually unlock the car using the key. Please help

You can recharge the battery from underneath using a battery charger, red lead to the big wire on the starter and the black wire on a clean bolt or body part.

What about your spare keys? They come with 2 or 3.

Then once it is charged, use and inflatable airbag and open the door a little.

https://www.google.com/search?q=porsche+cayenne+keys+locked+in+car

..

start by scanning vehicle for trouble code --fixing battery issue --resetting or reprogramming fob/security system

is the car battery still charged? is the transmission in park snapped in place , steering wheel is locked? key is all the way in and will not come out when in off position or is it frozen and straight up and down?
try to use spare key to unlock car and reset alarm antitheft disengage?
try opening keyfob and replacing battery?

Your going to have to put in the code for the keyless entry. You may be able to find it in the owner manual. If not, you will probably need to call the dealership to get the code.

I s your battery dead? do your headlight work? do they dim when you try to start it? Is your alarm turned off. If you have a key fob alarm control is the battery dead in it? Try pushing the lock-unlock button, does it work? press unlock and try it again. Is it in park or is the clutch pedal depressed?
Let me know. Lee

unlock the door then press the lock button on remote and hold down for 20/30 secs.manual does say hold button.....

Insert key into door barrel or ignition lock and turn key, whilst doing this press the unlock/lock button, the led on the dash should flash to indicate this has initialised the key to the car, then remove key and test operation of remote. If this fails then a new remote plus coding to the car by your dealership is needed

you might be using a valet key which prohibits use of this lock. try another key

Emergency operation of rear lid
If the rear lid cannot be opened with the radio
remote control (e.g., if the battery of the remote
control is dead), the emergency operation must
be performed:
1. Unlock and open the driver's door with the
vehicle key.
2. Switch on the ignition so that the alarm system
will not be triggered.
3. Check if the TAILGATE function is activated in
the multi-purpose display of the instrument
panel.
Please observe the chapter “TAILGATE” on
Page 119.
4. Press the central locking button in the armrest.
The rear lid is now unlocked and can be opened
with the unlocking handle