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I need to power two 12 V LED lights (1W - forward current @ 0.083 A) and a small piezo buzzer all in parallel (unsure about the current, tried to measure it with multimeter, but get nothing...).

Originally, I tried to build the battery with eight 1.5V AA cells, but it turns out to be too big for my use. I'm looking for another compact, lightweight battery to power the circuit and two possibilities come to mind:

  1. One cell 12 V A23 Energizer
  2. Stack of four Coin Lithium 3V Batteries, 2025

They have pretty much the same size and price. Which one would be able to power my circuit the longest, and for how long? I didn't get much from the datasheet.

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Neither is very good for your intended task, but the coin cells are better than the A23. In the datasheet for each, you have the Typical Capacity spec (Capacity in milliamp hours at a given load) as well as some information on Load vs Capacity or Voltage Drain vs Capacity.

In short, the A23 is typically 55 mAh, when drained at 2mA (0.002A) (Maybe 0.2mA, considering the 20kΩ load, faulty datasheet dropping the leading decimal point?). Yet has only 25 mAh at a 15mA load. The CR2025 typically has 163 mAh at nearly the same load as the A23. While the discharge characteristics might not be the same in theory, in practice if everything else is equal, you will get 3 times the capacity.

Not knowing how you will actually power the lights, two 83mA lights is 166mA, so if you power them straight on 100% of the time, you will get considerably less than 1 hour life out of the CR2025s.

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