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I have this electronics that uses 3V rechargeable coin cell battery (ML2032) to power the RTC when the system is off. When the system is powered on it'll trickle charge the battery instead.

I'm looking for ways to allow the usage of regular non-rechargeable CR2032 battery instead. One way I see people doing on Amiga, which also uses 3V rechargeable battery, is to simply add a Schottky diode in series. However, I wonder if there is something even better. To me a voltage drop of at least 0.15V is a lot for a 3V battery.

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marked as duplicate by PeterJ, tcrosley, Daniel Grillo, Ricardo, Chetan Bhargava Jan 30 '15 at 6:52

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  • \$\begingroup\$ The meaning of your question is somewhat unclear, but you can wire a bipolar transistor in a simple circuit which creates a diode with low forward voltage drop. (I don't recall the circuit offhand, though, since it's been over 40 years since I worried about this.) \$\endgroup\$ – Hot Licks Jan 29 '15 at 0:52
  • \$\begingroup\$ Without seeing the specifications, I can't be 100% sure, but it is extremely common in industry to use a diode in series with a coin cell for RTC. Note: it is a best practice to have at least two current limiting elements in series. The diode can be one. The second one can be a resistor. Choose a resistor value so that the drop is negligible during normal operation. Put a cap on the RTC side of the resistor. \$\endgroup\$ – mkeith Jan 29 '15 at 17:49
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The 0.15V drop is acceptable if the RTC is specified to run at 2.8V, or make it 2.7V. As long as these Lithium Coin cells are not completely depleted, they stay above 3V (fresh from the Box: 3.2V) quite well.

If there is a dedicated resistor for trickle charging that is not used in the circuit otherwise, just remove it, though.

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