i was saying if your alternator was charging low the OBC would recognize it, but i'm not sure.
the correct way to test a battery is to load test it with a battery tester.
another DIY way is to turn on your head lights, and then start your car.
if your car is hard to start (turns over slow) or the headlights get real dim while you are starting your car then most likely you rabttery is getting weak.
"we stared perfection in the eye, perfection blinked" BMW