What does 100% battery health and a cycle count of 47 mean for my iPhone 16 Plus?

It means it’s fine.

You are not going to maintain either the battery health or the cycle count. The cycle count is how many charge / discharge cycles have taken place. The battery health is an estimate of how much of the original charge capacity is left. All rechargeable batteries lose their ability to hold a charge with time and use. It’s inevitable.

When the battery health reaches 80%, the battery should be replaced.

Don’t obsess over either one. Just use it and charge it as needed.

On average, the Battery Health will decline about 1% for every 50 Charge Cycles.

So, when you have reached 100 cycles, the battery will be at about 98%.

When you have reached 500 cycles, the battery will be at about 90%

Replace the battery when it id down to 80%