UPSs still typically use lead acid batteries. These don't particularly mind being at ~100% SoC for years at a time (they
like staying charged), which is very good for this application.
And it's easy to keep them at around 100%. For instance: For a nominal 12v battery, one can very nearly just feed it 13.8v (plus or minus some temperature compensation) and have results that are actually pretty good and close-enough to 100%.
And when things go very wrong, lead acid batteries tend not to catch on fire.
It's a natural fit for UPS duty.
The lithium batteries in cell phones are a different thing. They hate being at 100% SoC and degrade fairly quickly in that state.
They can be pretty happy at around 50% SoC, but it's hard to actually keep them there because of the way the voltage ramps [don't] work with lithium chemistries: It's almost flat through the middle of the curve.
And cell phones don't let us do that anyway: It'd be great if there was a "Compute mode: Just do your best to keep this battery near 50%" setting to click on, but there is not. (And we could hack that in, except: We don't own our phones.)
And when things go wrong, they can become exothermic in ways that are not exactly ideal for an unattended device sitting on a shelf.
And it's easy to keep them at around 100%. For instance: For a nominal 12v battery, one can very nearly just feed it 13.8v (plus or minus some temperature compensation) and have results that are actually pretty good and close-enough to 100%.
And when things go very wrong, lead acid batteries tend not to catch on fire.
It's a natural fit for UPS duty.
The lithium batteries in cell phones are a different thing. They hate being at 100% SoC and degrade fairly quickly in that state.
They can be pretty happy at around 50% SoC, but it's hard to actually keep them there because of the way the voltage ramps [don't] work with lithium chemistries: It's almost flat through the middle of the curve.
And cell phones don't let us do that anyway: It'd be great if there was a "Compute mode: Just do your best to keep this battery near 50%" setting to click on, but there is not. (And we could hack that in, except: We don't own our phones.)
And when things go wrong, they can become exothermic in ways that are not exactly ideal for an unattended device sitting on a shelf.