I have a 2012 Mercedes Sprinter 2500.

I had a no start morning a couple times in the last few weeks and finally the battery would hold no charge. I took it in and was told it came back as need to replace, so I did so. Low and behold the van dies after a short drive. The new battery was not being charged. I charged the new (dead) battery and took a multi-meter to the battery with the van running and found the voltage to just drop from 12.6 volts down and down. At this point I believed it was either a problem with the y-cable that connects the alternator to the battery or the alternator itself. I took the multi-meter to directly to the alternator and found it to put out 11.80 volts at idle and 11.83 volts at around 3000rpm. My question is, should I just replace the alternator or do you think there could be another issue?

Thank you for any help you can provide!

2 Answers 2


11.8 volts is too low, you need at least 13.8 volts of output to charge your battery, preferably 14.5 volts give or take .2 volts. It sounds like your alternator is faulty, or possibly you have a loose belt not giving full contact. If the belt tension is good and the belt itself is not degraded then your best bet is to replace the alternator.

  • That's what I thought. The belt doesn't appear to be slipping and makes no sounds. Thanks for the input.
    – Caleb
    Commented Mar 15, 2019 at 20:27
  • Another odd thing though. I'm not getting any dash lights (the red battery) or check engine light. From what I've seen with the sprinter they usually show up if something is wrong. Any thoughts?
    – Caleb
    Commented Mar 15, 2019 at 20:31
  • @Caleb do you have wiring diagrams? I’d check all the charging system circuits before you do the alt. Also check to see if the battery has to be registered with the pcm like on some VAG and BMW cars. If it does you may kill a new alternator/battery.
    – Ben
    Commented Mar 16, 2019 at 13:05
  • I suspect you aren't getting a light because the alternator isn't completely failing, it's still producing some power @Caleb.
    – GdD
    Commented Mar 16, 2019 at 15:20

Before splashing out on a new alternator check the earthing strap to the engine as these can present similarly but cost a lot less if they are worn.

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