1) Test the battery with a multi-meter. Set to 20V - if it doesn't show 12.3 V it's the battery. If the battery is 8 months old it doesn't mean it wasn't made 2 years ago. Could be a short in the battery, they separator could have a hole creating a short between + and - side. of lead grid. 2) If battery is OK, it could be something else. Get a code reader OBD II. the connection is under dash under steering wheel. See if it's pulling any codes. My 2016 did something very similar. In my case my, it was a fuse. 3) if the battery is bad and it kills another battery it's likely the starter, but the OBD II reader should give you a code. The starter is pulling too many amps. It should only take about 10 min for the altenator to fully recharge the battery. You may want to look at a AGM (glass matte) more expensive if the vehicle sits a lot.