Hello allen_jar,
If your AirTag is still showing low battery after replacing it, let's make sure you inserted that battery positively side up and followed the steps below to do so:
Replace your AirTag battery
1. Press down on the polished stainless steel battery cover of your AirTag and rotate counterclockwise until the cover stops rotating.
2. Remove the cover and battery.
3. Insert a new CR2032 lithium 3V coin battery (available at most electronic and drug stores) with the positive side facing up. You'll hear a sound indicating that the battery is connected.
CR2032 batteries with bitterant coatings might not work with AirTag or other battery-powered products, depending on the alignment of the coating in relation to the battery contacts.
4. Replace the cover, making sure that the three tabs on the cover align with the three slots on the AirTag.
5. Rotate the cover clockwise until it stops.
You'll find these steps here: How to replace the battery in your AirTag
Let us know how it goes.
Cheers.