[abofh]

Ermm, most phones and computers cannot be completely powered down. Either by nit-picking (CMOS clocks) or soft-switches (ACPI, soft button power-on), there's always some voltage in the system unless your PSU comes with an actual hard power switch (and even then, again, CMOS).

They consume a lot less power, but leave an 'off' phone in a drawer for a month starting at 100%, it will not be 100% when you 'turn it on'.

[JoeAltmaier]

In low-power mode even those microcontrollers are using just nA (yes that's nano-Amps). Vs 100's of mA in operation. So the battery life goes from hours to what should be decades.

I'm thinking the battery goes dead because of leakage currents through the rest of the circuits, which were probably not designed to the nA standard.

A solid-state Off switch would also need a good silicon device to cut current consumption at the battery. Which also costs something.

[unwind]

I understand and agree, but the use-case is a bit skewed since that's not even true for a bare "naked" battery or cell.

They all self-discharge [1], some chemistries more than others of course but phone batteries certainly do.

[1]: https://en.wikipedia.org/wiki/Self-discharge

[Retric]

Self discharge is easily an order of magnitude slower than the power draw of these devices while seemingly off.