Battery light at redline (Mazda5). Belt?

[IamFODI]

For reasons I think are probably obvious, I don't redline our Mazda5 as much as I redline our other car. But when I do, the battery light comes on. Am I correct that this is probably because the belt is slipping? Anything else to check?

 

[negusm]

Voltage regulator in the alternator is probably cutting out due to too many RPMs.

Or belt is slipping.

 

[IamFODI]

Same thing happening with a new belt and battery. So, I guess it's the alternator – either by design or because it's aging.

Not planning to poke at this any more because I've decided to stay at least a few hundred RPM below the redline for other reasons, and there are no other symptoms. But if I ever replace the alternator, I might test it again just for kicks...

 

[IamFODI]

After seeing this happen several more times, I'm pretty sure the magic RPM is 4000. If I spend more than a few seconds above that, the battery light comes on and stays on until I drop below 4k. Never seen the battery light come on below 4k RPM.

Months ago, I ordered a Bosch reman alternator for $115, which seems to my barely-informed eye like a great price for a solid quality product. Unfortunately it keeps getting delayed; current ETA is late March. But the battery seems fine so far, even despite some accidental abuse, so I'm not in a hurry to look for another alternator. If anyone disagrees with any of this reasoning, I'm happy to hear about it.