2001 c 240 electronic key issue
 

hi guys, need help
My c240 remote key is acting up. it will not lock/unluck the car unless i keep trying for like 10 min. Soon as it opens the doors, it works fine as if nothing happens before. also I notice that after driving the car, the key perform well.if I let the car seat for a while, then i have to keep tring for another 10 min. I resynched the key a couple of time but that does not seem to fix anything. I put brand new battery in there put the result remains the same. I remember, that issue started after i came back from a 1 month vacation. I had to jump started the car. Can a defective car battery be the cause of such issue? Please help????