Being an expert in the realm of hard-water fishing, I found that a schedule of exercising the 12-volt, sealed-lead battery for the Vexilar, extended it’s life three years longer than my compatriots whom put theirs on the shelf and left them unattended during the off season. It resulted in higher performance in longevity in actual operation, and overall component usability.
I have applied this technique since the days of NiCads. I guess that’s where the “rule” stems from.
Today, more sophisticated and more portable technologies are using “Lithium-Ion” batteries. Does exercising these batteries extend their lives as well?
Lithium ion likes the opposite treatment to NiCad. Keep them fully charged, leave them on the charger when not in use, and top them up immediately after any use and they’ll do better. Deep cycling shortens their lifetime.