Battery Problems

Hello! I just searched the forum, but couldn’t find anything that could solve my problem, so I hope for you Escort XR3i BJ 92 If the car is standing for several hours, it won’t start any more. The window lifters, the light, the radio goes all the way. If I then do start-up help, or recharge the battery, it starts without any problems. Even if I let it roll down the mountain it starts well. If I turn it off and start a short time later it usually works. The only thing I’ve changed lately was the changed clock, which now has blue LEDs. According to ATU Test, the battery is perfectly fine, is also only one year old. Is it the alternator???? Already thanks for the answers that hopefully will come soon.