I'll add this information from another thread. Watch that your charging voltage sometimes exceeds 14.0 volts. If it doesn't then it may have a partial failure as described by Dennis/Mein Sprinter.
This is the text from post #51. Click on the redirect arrow far below to be taken to the other thread.
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I replaced the alternator on the 2006 today.
I've been noticing that after starting the engine the voltage would often remain low for a time before the excitation would kick in. My first clues were that the cabin blower speed and wiper speed would often be reduced. Dimmed headlights for a time at night was a more obvious clue. My voltmeter is included with the added USB charge unit so it is switched to avoid the USB unit drain. I started switching the VM on which verified the longer than normal and intermittent timing on the charging kicking in. Revving the engine a bit had no effect on the lag time.
The 2006 VM also showed that the charge voltage was only hitting 13.9 - 14.0 volts. The 2004 always jumps to 14.1 - 14.2 initially [after the normal approx. 5 second delay for excitation]. That seemed a hair low to me. I just needed to replace a 4 year old battery. (Only 12.1 volts after sitting overnight.) It could be related to the lower charge voltage not topping off the battery.
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Added:
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While having the 10 yr old weak alternator replaced at Dennis during a drive thru health check before a long trip we had him change the VARTA to a Super Start (49PRMJ):; 825 CCA; 1000 CA; 12 Volt;.
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Cheers...
Alternator failure according to Dennis techs was stated as;
" Alternator has massive amounts of diode ripple causing it to no longer properly charge like it should. With no load the Van charges at 14v but cannot maintain 14v once loads are introduced into the equation"
Cheers...
DIY troubleshooting tip.
Because DIY types likely lack the more sophisticated equipment Dennis uses, if you notice that your charge voltage never exceeds 14.0 volts it is probably time to investigate your charging system. I'm not suggesting that the alternator is bad. I'm suggesting that never charging above 14.0 volts suggests a system problem.
The 2004 now older Bosch150 amp alternator of jumps the voltage up to 14.2 - 14.3 volts before tapering down. The 2006 with new Bosch 150 amp alternator now jumps to 14.2 - 14.3 volts before tapering down. That isn't every time, but predictably with the first start of the day.
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The choices that I saw were to take the time to try to troubleshoot the excitation circuit, just replace the excitation/brush assembly, or replace the alternator. At 14 years old/184,000+ miles on the alternator wear parts I felt replacement was the best course. I watched for 150 amp Bosch alternators [an upgrade over the 90 amp] and found one for good price.
By using this Write-up (that one of the wonderful members here on Sprinter-source provided) replacement went pretty well.
Some additional comments.
My admiration goes out to anyone who does R&R the alternator without removing the TR. The clearances with the TR out are bad enough. It is worse, if not impossible, with the TR and bracket in the way. Maybe leaving the TR alone with a like for like 90 amp swap would work????
The 90 amp Bosch unit falls out with little problem. The 150 amp replacement went in with some fiddling. (The TR bracket was loose and had been moved over out of the way. No additional parts or brackets were removed. It did take getting the 150 amp unit into a specific position to move it up into place.)
I don't recall this on the 2004. The 2006 upper *non-bracket* bolt wouldn't pull out far enough for removing. It bumped into a bracket which stopped the travel. I left the loose bolt in the hole. After the old alternator was out I set the alternators next to each other and transferred the bolt over to the new unit. The method has the additional advantage that it keeps the "Vee" notch of the mount casting in proper orientation.
Other than that I followed the basic procedure in Post #1.
After replacing the alternator the charging voltage now jumps right up to 14.1 - 14.2 volts after the normal excitation delay built in to the control circuit design.
I probably won't bother with replacing the excitation/brush unit on the removed 90 amp alternator. As an aside, the removed 90 amp unit free running clutch is still working fine. No bearing noises.
If anyone wants it for free, local pickup only. Nope. I donated it to a local automobile electric rebuild shop.
Unrelated. While the TR was out I cleaned up around the seam, sanded a bit, and applied a 2 part epoxy putty worm around the entire seam. I don't expect that the 2 part putty will adhere well to the thermoplastic. I pressed the putty on and overlapped the ridged edges with the idea that it would act as a clamp of sorts to help to minimize deformation of the plastic. I believe that the 2006 TR is OEM FWIW.
vic
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I replaced the alternator on the 2006 today.
I've been noticing that after starting the engine the voltage would often remain low for a time before the excitation would kick in. My first clues were that the cabin blower speed and wiper speed would often be reduced. Dimmed headlights for a time at night was a more obvious clue. My voltmeter is included with the added USB charge unit so it is switched to avoid the USB unit drain. I started switching the VM on which verified the longer than normal and intermittent timing on the charging kicking in. Revving the engine a bit had no effect on the lag time.
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vic
I didn't know it was fuel injected. 
