What's the normal lifespan of an alternator? (Gen 3)

Like so many others, my Jimny squeals on start-up. Frequently on cold / wet days and especially when under electrical load (I can "fix" it by turning off the heated windows..!). So the belt is slipping, which could indicate a few things.

First being that the belt simply needs tightening. I went out and had a look, seemed tight enough, but I still tried to tighten it further anyway (annoyingly fiddly job but did it). Problem still there. The condition of the belt itself looks fine and the battery was replaced just a few months ago (before I purchased the vehicle).

So that leaves me thinking it could be a pulley or the alternator / alternator bearings. Since it's only on start-up that to me says it's maybe the alternator "pinching" as it tries to re-generate the lost energy from the start-up?

Given all this, what is a normal life expectancy of a Gen 3 Jimny alternator? For reference mine is a 2007 ~75k miles. I'm thinking it's probably long in the tooth enough that it could be what's ailing it. Especially given I have a head unit and dashcam up front drawing a bit more power.

Hmm, actually, while I am still interested in the thread title, I dug through my service history. I can see the aux belt was last done ~5 years ago and the power steering ~4 years ago so I'm gonna replace both of them before worrying about my alternator.

The car has only done 20k miles in those 5 years so would explain why the belt looks in reasonable condition but it has been long enough that it could just be degraded.

As you say it is also worth looking at the pulley. Shine a light on it when it is running and in most cases you can see a clear wobble in the pulley

Martin

Micro vee belts like the jimny uses dont need nearly as much tension as a standard vee belt. (The AC / PS belt just uses a spring tensioner) An enthusiastic young mechanic apprentice may have cranked the daylights out of the alternator belt on your last service and given the nose bearing on the alternator a hard time, causing the bearings to fail prematurely. 
I have this same problem on my other vehicle, a 1984 Chevrolet C20 with a 6.2 v8 diesel. It just uses a standard vee belt, and the way its set up the vibrations/ harmonics from the big diesel means that to tighten the belt where it won't squeal /slip meant I was changing nose bearings once a year at least. I swapped the nose bearing (after a bit of machining) with a double row bearing and so far seems to have helped. Chevrolet went to microvee belts later for this reason. 

​​​​​​If you're confident with mechanical stuff I can't see why you couldn't replace just the bearings if that's the issue. I've haven't had a jimny one apart so others could confirm, most others I've had in bits used fairly common bearings.  Assuming of course, your alternator is functioning as its meant to electrically. 

I have a similar issue with belt squeal at start up with a heavy load. I tried changing the belt but that didn't help. I think the belt routing is a bit marginal. There is not much belt wrap angle around the pulley which makes it prone to slipping.

If it's more of a chirping or a screaming noise it could be the idler pulley bearing. Offer it rotating assemblies a touch with an engineers stethoscope and it will become apparent where the noise is from. A long bar pressed to the ear also works. Be careful though as with the engine running it will want to grab at loose clothes and unwary hands.