Door locking issue with key fob

[QasamDar]

My A5 has stopped locking with the keyfob. When i press the lock button i can hear a sound to indicate its locked and the alarm will arm however the car door will remain unlocked.It will lock if i use the key inside the fob.I have tried changing the battery however it made no difference. If i try lock it with the keyfob the headlight will no longer flash however if i lock it with the actual key and then press the button it will flash. Any help will be appreciated as i feer taking it in and the mechanoc trying everything under the sun when it coukd be simple. Also my passanger door does not open and the handle feels like its loose. I have read many post about this being a common issue but i wonder if the new issue is connected. This was fine when i bought the car however started shortly after purchasing.

[A5guy]

how old is the car battery? any warnings for this? sometimes i have seen my A5 shutdown various systems (after not being used. for a few days) if it was scanned it shows some "power management" mode 

[QasamDar]

The battery im not sure but that is a good shout as i do get a battery low will charge when driving warning. Is there anyway to test if its the battery causing this other then buying a new battery? I dont have any issue with starting the car it will always start 1st time.