A search didn't bring up this information so I thought I would post it for posterity. I got a cryptic pop-up message twice today on my short commute home. "Car needs service. Car may not restart" It cleared on it's own so I looked into it a bit and got some suggestions it might be the start of troubles with the 12 Volt battery. The Model S has the battery located near the passenger wheel well but I located it in my P90D just left of the main fuse box in the behind the frunk. If you remove the shielding between the frunk and windshield, you'll see the fuse box in front of the driver. To the left and down, you'll see the battery. Service recommended that I wait and see if the pop-up warning continues to appear. The battery health indicator on the battery is green, which indicates it's in "good health". It has been cold lately and my commute doesn't allow the main battery to warm up enough for full regen, if that matters. If there's any issue, I'm sure Tesla service will handle it.