How you treat rechargeable batteries to extend their life really vary depending on the chemistry of the battery as well as the smartness of the charger.
Hearing aid rechargeable batteries are usually of 2 types, the Lithium Ion battery, or with the Z Power system, a Silver-Zinc type. Lithium-Ion batteries in general can be topped off at any time and doesn’t need to be depleted before charging. I have no idea what the Silver-Zinc type requires, but I don’t see any special warning when I review the Z Power website for special handling to prolong its life.
For cell phones, the charger is smart enough that if you leave it connected it’ll stop charging, so you don’t need to worry too much about that killing your battery longevity. And cell phone batteries are mostly lithium-ion or lithium-polymer type that can be topped off at any time.
The factors that would reduce Lithium-ion battery longevity is if it’s always at near 100% or near depleted. That’s why most manufacturers store the battery is 50% charged when they come to you. That’s the happiest state for Lithium-ion batteries -> 50% charged. 100% or near depletion stresses out the battery more than at 50%. If you have a laptop that you keep plugged in all the times and allow it to stay at 100% charge most of the times, the battery won’t last very long. Same with when you keep your battery at almost 0%, although this happens much less often because the device would be useless at low battery charge anyway.