Battery light flickering on startup

[E53fan16]

Hi guys,

I noticed Saturday that my battery light has been flickering on startup. It continues to do this now. Is this a sign for me to get a new battery, or is the alternator slowly on its way out?

I use a Bluetooth transmitter that plugs into the cigarette lighter up front that gives me my battery levels. Prior to starting the car, it's 12.5V and while the car is running it's 13.8V. This seems within range. I have a small road trip coming up this Thursday so just trying to get an idea of what may be going on.

Thanks in advance.