[scruple]

I've seen a handful of his videos but not the one on smoke detectors. I replaced our batteries this week (once one of them chirps and I hear it, I replace them all, or else they end up with drastically different states of battery power -- which is at least a little bit funny... How do they all not drain power at a similar rate?) and it got me thinking about how very little I understand about these critical devices.

[chipsa]

Slight variations on the electronics give slightly different characteristics, and hence different power draws... but also, the batteries are also going to have slightly different capacities, so you have random amounts of power draw clustered around a given value, and random amounts of capacity also clustered, so combined you might end up with a detector drawing 70uA on a 540mAh cell, and one doing 50uA on a 560mAh cell, but the cell voltage they start chirping at is exactly the same.

[dotancohen]

  > How do they all not drain power at a similar rate?

I do not know if each smoke detector drains power at a similar rate (maybe some are in hotter or colder locations in the house), but I do know that the total energy in each battery can vary as well.