Last night I left the dome lamp(s) on in the car and the door ajar. It was on for over 12 hours. I began driving earlier and drove fast up an extremely steep hill and the battery/alternator warning message came on atop the hill. The car began losing power features and ESP/ABS/BAS lights came on, power window moved slowly and illuminated ESP/ABS/BAS when I pressed window switch. I have never had this occur before. Belt is tight and appears OK. Battery is a year old MB battery. Wondering if this indicative of low voltage from lamp being on and hill climb straining voltage levels or related to something else.

Thanks.

 

trying to guess at the health of the battery based on secondary indicators isn't going to
pinpoint the problem. MEASURE the voltage, both at rest as well as under load. Also,
based on your description of the potential cause, if you have a flooded lead battery, I'd
look inside each cell for visual confirmation of the fluid level and perform a hydrometer
reading of the specific gravity of the acid. doesn't matter if the battery is one year old.
you've induced a potential deep discharge condition by leaving the light on. so the
health of the battery is now suspect.

important: the alternator is only designed to perform maintenance charging of the battery.
it was never meant to charge a deeply discharged battery. it would be a GOOD IDEA to
trickle charge the battery with a 10 amp stand alone battery charger overnight (at least)
as well as to perform the above checks.

your neighborhood auto parts store will frequently do a battery health check for free

 

When I've had that message it was a bad alternator. Got a new one at Advance Auto for about $130 and has been fine for the past 4 years.

 

Its a bad alternator.

 

Very easy fix and readily avsilable part