I have a garage remote that stopped working. I changed battery and it worked again, but only for a few days.

I measured the resistance between the poles of the battery terminals and it was about 760ohms. My assumption is that it should be much greater (ideally infinite). So I noticed that what it seemed to be a capacitor (a surface mounted spec, with a yellowish band) and it had exactly the same resistance, so I thought that either that was not a capacitor or it had failed (because the resistance should be also zero).

To complete the picture that capacitor was just after the battery terminals). I decided to remove it.

The end result is that the remote keeps working and resistance between battery terminals is now off the scale. Hopefully it will not discharge as fast.

What was the purpose of that capacitor? (If it was a capacitor in the first place)

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    \$\begingroup\$ why downvoter why? \$\endgroup\$ – gurghet Jan 25 '19 at 9:48
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    \$\begingroup\$ Repair questions are off-topic. Without a schematic, impossible to answer. You ask about a component and you're not even sure what type of component it is. How are we supposed to provide a proper answer then? \$\endgroup\$ – Bimpelrekkie Jan 25 '19 at 9:51
  • \$\begingroup\$ You would be well-advised to read the FAQ's available before posting. \$\endgroup\$ – Solar Mike Jan 25 '19 at 9:51
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    \$\begingroup\$ Well this is not the first time I see a capacitor between battery terminals so I assume it's well known what they do. Also it's not a repair question I do not ask how to repair stuff. \$\endgroup\$ – gurghet Jan 25 '19 at 9:52
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    \$\begingroup\$ And you doubt it is a capacitor? It could be a reverse battery protection diode as well. \$\endgroup\$ – Bimpelrekkie Jan 25 '19 at 9:53

It's a reservoir capacitor, the lithium button cells used in remote control have a high internal resistance, the capacitor (if intact) has a low internal resistance and can supply surges of current. this the remote to operate transmit stronger signals than without it.

I recommend replacing the broken capacitor with a new capacitor 10uF is probably about right.

  • \$\begingroup\$ This is probably more correct \$\endgroup\$ – gurghet Jan 25 '19 at 11:23

this could be radio frequency suppressor capacitor to avoid radio interference to other sensitive gadgets nearby.

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    \$\begingroup\$ This is more of a comment than an answer. I know that you, as a new user, can't post comments to questions yet – but you will be able to, in short time. Ask a few good questions, write a few answers (which actually are answers, not just comments), and you'll easily have the points necessary. \$\endgroup\$ – Marcus Müller Jan 25 '19 at 10:05
  • \$\begingroup\$ your answer is correct! \$\endgroup\$ – gurghet Jan 25 '19 at 10:11
  • \$\begingroup\$ @gurghet how do you know its correct? I was just about to write a very different answer. \$\endgroup\$ – Steve G Jan 25 '19 at 10:13
  • \$\begingroup\$ @SteveG similar to Jasen's? \$\endgroup\$ – gurghet Jan 25 '19 at 11:26
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    \$\begingroup\$ Yes. The internal resistance increases as the battery ages so the associated problems get worse. Your new battery will have a low internal resistance and so appears to work, but without the capacitor it may stop working prematurely. Replace the cap and you should be Ok. \$\endgroup\$ – Steve G Jan 25 '19 at 11:34

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