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Your car has a smart charging system that saves gas by limiting battery charge.
Once a while the voltage control quietly disfunctions and then toast the prefuse module with (90A + 25A x 14.9V =) 1700.Watts.
Once that keeps repeating the tinned bras is oxidized into a poor conduction that drops more or less voltage based on system load.
None of the Mercedes specialist deliver cheap repairs. So DIY'ers do their own maintenance when possible. You should collect data to see why your engine is has bad days.
Last edited by CaliBenzDriver; Apr 25, 2026 at 03:53 AM.
Your car has a smart charging system that saves gas by limiting battery charge.
Once a while the voltage control quietly disfunctions and then toast the prefuse module with (90A + 25A x 14.9V =) 1700.Watts.
Once that keeps repeating the tinned bras is oxidized into a poor conduction that drops more or less voltage based on system load.
None of the Mercedes specialist deliver cheap repairs. So DIY'ers do their own maintenance when possible. You should collect data to see why your engine is has bad days.
Ok scanners cost more than a tank of gas. Luckily it is free to display 'battery sensor" data.
Battery sensor displays both voltage & current
See youtube for video on how to enter "shop menu" before starting your engine.
> Test drive steps...
set display to show battery voltage
drive conditions: non-stop 30mn daytime
watch normal voltage steps: 14.9... 13.7... 12.6V
Pay attention that running voltage never gets below 12.5V with high Amps greater than 25Amps
Report testdrive : pass/fail.
Did you see low voltage below 12.5V... 12.3V.... 11.9V.... 11.7V drains both of your batteries?
High currents oxidize the prefuse pathways with high heat from drop voltage.
Last edited by CaliBenzDriver; Apr 25, 2026 at 02:02 PM.
