Avionics tech here,
Our fleet had some issues with a batch of G5 batteries not long ago. I found that the date range from 2020-2022 weren't so good. Most would not even take a charge and we're dead as a doornail. Garmin support was pretty helpful and RMA'd out about 10 batteries. It's worth a quick email to see if they will warranty out a battery.
Another note, when applying power to the aircraft, you can hold the power button and the depress on the selection knob and enter diagnostics mode. From there, find the diag tab and scroll until you find battery diag, this will show your battery health and charge state. Hope this helps!
