my 2010 c63 battery light came on this morning(very cold around 5 F)

and I was trying to use the engineering mode to find out the alternator is charging which the voltage is staying at 14.5+ volts, but the weird thing is after I start the engine the voltage stays at 11.5 for like 15-20 seconds, then it quickly come up to 14.5 after.

I was just wondering is this "15-20 seconds" normal?


p.s the battery light didn't come back on again on the second start of the engine


million thanks

 

I think that it takes the alternator a while to get up to speed and start generating a charge. The 11.5 would likely be battery voltage until the alternator kicks in and switches it to alternator voltage of 14.5.

 

Agreed that 11.5 is the battery voltage. From my experience thats getting toward the low band of what it takes to start my car. Mines a daily driver so about every 3 months I have to throw it on the trickle charger because of all the short trips I take and I'd rather do that than need a jump. Also with it being cold it probably took a bit more juice to get it going.

 

I think below 11.5 battery voltage the car disconnects the starter circuitry and the car goes dead and all sorts of weird warnings come up on the dash. You will then need to charge or replace the battery to get going again. Happened to me once for whatever reason the charging system did not maintain the battery voltage. I have a CTEK charger and brought the battery back to full charge and then but it through a recondition cycle and it has been good since. I do put it on the charger to trickle charge when it sits for long periods to keep the battery maintained.