iPhone 13 Battery Health dropped

Battery decline is not linear. The battery might not drop at all for several months, then drop 3-4% the next month.

Your battery is operating normally. It will go about 2 years from the purchase date before it will need to be replaced.

All that you need to remember is to replace the battery when the Battery Health drops below 80%.

No need to babysit the battery. It won't help, and will simply tend to make you nervous when there is no reason to be so.

Since the iPhone 13 was launched 4 years ago and discontinued more than a year ago, the device was not purchase at Apple or Authorized Apple Seller so it would be difficult to know if the battery had previously been replaced with a non-genuine part or if the battery was "boosted" when you purchased it to appear new.

A genuine battery on an iPhone 13 is expected to last 500 charge cycles before it needs to be replaced when the battery health drops below 80%. The drop in battery health is not linear and some months may not drop at all and other months will drop more. The calibration of the battery only occurs when it has been allowed to charge to 100%, so if you are manually unplugging the phone before it reaches 100% then you may see the larger than expected drop after that calibration has been able to be performed. Nothing wrong with seeing a 1% drop per month on average though.

95% after 5 months is perfectly normal. As a matter of fact your iPhone is expected to drop 1% battery health per month. But note it doesn't drop perfectly each month, it can drop a few percent in one month, then stay steady the rest. So while it may seem abnormal it dropped a few percent abruptly, if you look at the bigger picture it's right on track.