Sleep current
also: quiescent current · standby current · deep sleep · Iq
The current a battery product draws while idle; in devices that sleep most of the time, it often decides battery life more than active power does.
A sensor that wakes for a few milliseconds every minute spends almost its whole life asleep, so the difference between a few microamps and a few hundred microamps of sleep current can mean years of battery life. Sleep current includes the processor's sleep mode, every regulator's quiescent current, leakage through pull-up resistors and voltage dividers, sensors that can't be powered down, and the battery protection circuit.
Battery life is roughly usable capacity divided by average current, where the average is weighted by the time spent in each state.
Where it bites: one forgotten LED, a voltage divider left connected, a peripheral left enabled in firmware or a regulator with high quiescent current can destroy battery life, and these problems often show up only when measured with a sensitive current profiler.
Founder takeaway
Set a sleep-current target for each subsystem, measure it on every board revision and firmware release, and treat regressions as bugs.
engineer review pending