[jmc]

With all the battery posts of late, and my recent bout of a weak battery, thought I'd check out how the onboard system actually does it's job of "maintaining" the battery ... using my existing battery as the guinea pig

1) Initial conditions

• battery (3rd OEM from Benz installed 04/11/18) tethered in AGM maintenance mode 12/22~12/28
• stopped maintenance charging on 12/28
• observed voltage periodically 12/28~01/14 (car dormant 12/28~01/20 no door switch activity)
• as expected the battery level decreases with all the telemetry systems always running
• drop was 12.76V to 12.63V

2) First drive

• 7.5mi trip over ~23min
• with systems "on" before ignition 11.9V (dropped from ~12.6V)
• ignition point 10.4V (cold engine dormant for 23 days / coolant 52F / ambient 53.6F)
• after ignition full charging profile during trip / never <14V

3) Second drive

• 7.5mi trip over ~27min
• with systems "on" before ignition 12.4V
• ignition point 12.2V (warm engine easier start / coolant 145F / ambient 77.0F)
• after ignition full charging profile during initial drive time
• until software "adapted" to battery's state of charge for remaining time (INTERESTING to finally see it !!)
• resting voltage at engine idle 12.6V

4) Comparison with new (unconnected) battery

• charged up the new H7 after purchase
• stopped charging left battery dormant not connected
• observed OCV (open circuit voltage) over time
• from 12/28~01/21 drop was only 12.87V to 12.83V (during same 12/28~01/14 period)
• self discharge is nice and slow