When you test a car’s battery, what are you doing?
You’re asking: how much energy can you store? How does that compare to the amount of energy you were designed to?
Over time, that storage capacity inevitably goes down.
Why?
In short, being a battery is hard.
Every charge/discharge cycle causes chemical and physical stress. Lead sulfate crystals build up, material flakes off from vibration, and internal corrosion occurs.
As these parts of the battery degrade, it loses the ability to hold a charge.
Without rest, so too does the human spirit see a reduction in storage capacity of love, joy, peace, and selflessness.