Currently, powerdevil implements Lenovo's conservation mode and the more generic battery charge limits separately.
Conservation mode is a simple toggle, on or off, and leaves the limit value unknown, sometimes 60% or 80% between devices. Charge limits are more generic and widely used, allowing the user to specify a range to stop charging at a value and start charging again at another.
The problem is that there is no ability for a single control to toggle all forms of battery protection charge limits. Users will often want to toggle them on/off (regardless of configuring the thresholds) depending on use case — if they're going on a long trip, they definitely want to be at 100%. At home or short-range use, they may want to observe the limits. The only way currently to toggle them on/off is to open the Power Management KCM and go to the Advanced Power Settings page.
In order to have a single action to toggle this on or off, we would need to support enabling/disabling charge limits altogether, with further settings if available (i.e. not on Lenovo) to configure the threshold values.
With this done, it would be incredibly useful to expose this in the applet, to quickly turn it on/off without navigating System Settings. I've undertaken preliminary UI work to this end before encountering this roadblock in the work/olib/batterymonitor-conservation-mode-toggle branch:
(Of course, the message below would be hidden when the switch is off)
@jpetso has informed me that this refactoring is an eventual goal — and I'll be happy to help on the applet side and with testing on a Lenovo (conservation mode) device.