Apple MagSafe decreasing my battery life

Are you referring to Battery Health percentage or are you referring to Battery Charge percentage?

Either way, The purpose of the MagSafe charger is to charge your iPhone's battery wirelessly. It also fast charges your iPhone 12 at the rate of 15W. It has nothing to do with reduction of Battery Health or the Battery Charge percentages.

iPhone batteries, like all rechargeable batteries, are consumable components that become less effective as they age. You should change out the battery once your Battery Health reaches below 80% which will take over 2 years to reach under normal usage. Until then enjoy your iPhone.

Here is some more reading on an iPhone battery and its performance ➔ iPhone Battery and Performance - Apple Support

Axel F.

Snoowy wrote:

Is using an authentic apple MagSafe charger decrease my battery life?.

Every charger will decrease your battery’s maximum capacity. The only way to not decrease maximum capacity is to never charge your phone. Batteries are consumables; they lose a little capacity every time they are discharged, then recharged. On average this works out to about a 1% loss for every 25 “full charge cycles”. As one example, if you charge the phone overnight, every night (and that is what you should do; it is a best practice), it starts the day at 100%. If it drops to 20% by the end of the day before you charge it again overnight that counts as 0.8 full charge cycles (20% to 100%), or about 24 full charge cycles per month of use. For this example your battery capacity will lose about 1% per month. Of course, if the end-of-day level is higher than 20% the capacity loss will be a little less, and if it is lower than 20%, or you charge it during the day, the capacity loss will be higher.