The battery health indicator will go down if you regularly don't use it on battery. Apple's documentation even says this in a round-about way in their support docs, and I can confirm that I have observed this behaviour.
Why? The "health" reading is the max the laptop will charge to (which can be either due to age, or due to the learned charging behaviour), which it will reduce like other third party battery apps to improve battery longevity.
Use it on battery a bit and the health will come up.
But at the end of the day - use it as you need it. If you don't use it on battery much, clearly you don't need the max battery capacity and so the Mac is reducing charge level to suit in order to reduce wear on the battery. Unfortunately this influences the battery health due to the way it is measured.
Why? The "health" reading is the max the laptop will charge to (which can be either due to age, or due to the learned charging behaviour), which it will reduce like other third party battery apps to improve battery longevity.
Use it on battery a bit and the health will come up.
But at the end of the day - use it as you need it. If you don't use it on battery much, clearly you don't need the max battery capacity and so the Mac is reducing charge level to suit in order to reduce wear on the battery. Unfortunately this influences the battery health due to the way it is measured.