Why is my radio-controlled clock lagging behind the correct time?

I received a radio-controlled wall clock that works on a battery (1x type AA/1.5V). Once the battery is in the clock, the second hand will start and both hands will rotate rapidly until 00:00. Then the time ‘stops’ for a few minutes. I assume that a check is then made via DCF for the correct time. Then the second hand starts again and both hands turn quickly to the correct time. Since a few days I notice that the clock is starting to run slower (about 1 min/hour). Although I like the function of the 2 buttons on the back and do not know, I have found that holding down the button for at least 5 sec, performs the same steps as removing and reinserting the battery. In both cases I get to see the correct time again, at least for a short time … But I have also discovered that replacing the battery with one with a higher voltage (i.e. less empty) has ensured that the time is now correct for longer. remains (at least 7 days at the time of this writing). I didn’t expect this last one! And so I now ask myself the following questions. 1) What/how does the 2 buttons work and ? 2) How is it possible that a radio-controlled clock runs behind the correct time? Even with a minimal delay of the seconds one should never reach 1 min/hour? From the fact that a battery with a higher voltage solves this problem, I draw the following conclusions: – whether the second unit is variable, depending on the battery voltage, – and/or there is periodic interim time correction via DCF at a minimum battery voltage. I’m afraid this problem is very device dependent, but I hope someone can give me an explanation for this. Thanks in advance!