Battery Health decrease within TWO MONTHS

Because batteries are consumable parts. With every full cycle charge, the health of your battery will degrade naturally. This is the chemical aging of the battery. There is only one direction Battery Health can go and that is DOWN. On average, users can expect a loss of 1 - 2% Battery Health per month. This is unstoppable, normal and expected. When the health of your battery dips to 80% or less, it will then be time to pay Apple to replace the battery. Until then, accept that your iPhone is operating normally and worrying over something which cannot be changed is worrying for nothing.

It is normal for the Battery Health to decline an average of about 1% a month, so your phone is normal and just fine.

After a year, the Battery Health will be in the 87-89% range.

Replace the battery when it is down to 80%