I posted the main thread in RF here https://forum.allaboutcircuits.com/threads/debug-on-434mhz-keyles-entry-buggy-electronics.204861/
but I think it may be a general electronics subject too.
Summary:
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Remote transmit well when internal LED is lighting well. First button push not make it lit normal, it needs more or sometimes many many more. 2 remotes, one used daily and one almost not used, both work bad (both made in 2007). Can be the car receiver or damaged part in transmitter (because is old not because is used - the not used remote works bad too - think of degraded capacitor).
Read details and give answers here https://forum.allaboutcircuits.com/threads/debug-on-434mhz-keyles-entry-buggy-electronics.204861/

Thanks.

 

The same thing happened to somebody I knew. The batteries in the remotes got old and weak. The lady was amazed when I showed her a button on the wall in her garage that also opened the door. 35 years she lived there and never knew about that button. Her retired son changed the battery for her. The really bad news is that those tiny batteries get old and weak.

 

The same thing happened to somebody I knew. The batteries in the remotes got old and weak. ...
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The really bad news is that those tiny batteries get old and weak.

Thank You MisterBill2 for answering. However, is difficult for me to catch the point, if you let me say that. You mean that the new batteries that I installed were also not good, even the voltage were higher, arround 3.3V for each (they are 2 for each remote)? It may be possible, but the remote consumtion should be few mA in use, and Isc for the batteries were about 80-100mA. I didn't expect a voltage drop on batteries when button were pushed; contrary: I saw that the led lit stronger and stronger after more pushes. Eventually I can think that the new batteries are too old (bought a foil of 10 pcs 1 yr ago) and get "awaiken" and give more power with using the remote? It happened to me but when the batteries get hotter in use, which is not the case here (same problem in summer as in winter, from my pocket (25C) or from car contact in winter (-5C). And after 20-30 min goes again back to sleep?
I hope you already red all details on the linked post specified above https://forum.allaboutcircuits.com/threads/debug-on-434mhz-keyles-entry-buggy-electronics.204861/

I could enventually rise the connections btw components, if they are not very clear on pictures, if you think it may give you more ideas of what happening here.
Please suggest me what you think I should do.

 

OK, I did not see a comment that you replaced the batteries. OK, with fresh batteries then something else will be the problem. Did you clean the battery contacts when you replaced the battery?? Some times there is an oxide build up on a battery contact.

 

Does the button on the remote switch power to the circuit?
If so then the switch may have developed a high resistance and multiple presses cleans the contacts.

 

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