Alternator dying?

[D1dad]

So after getting stuck last week I tested all the batteries in my cars. My 18 rogue tested at 85% battery health this summer but now only test at 36%. I put in a new deka flooded battery, not agm. I just took it for a spin with my scanguage hooked up and the alternator gives off 14.3 volts when started, then drops after a mile or two later to 12.9 and then stays there. I know Nissan uses the whole “smart charge” system. But 12.9 seems low. I even had the heater cranked up pretty good. Is this normal?

[VStar650CL]

Sadly, yes, Don't be surprised if it occasionally drops even lower. I saw the similar setup on a Sentra hit 12.3V during testing for a different issue, and it hovered there for nearly 40 minutes before suddenly jumping back up to 14.5V. Don't ask me what the engineers are thinking, I have no idea.

[D1dad]

Oof. I guess I never really paid attention to this before with any detail. This thing for the most part is short tripped, under 6 miles each way a day. The occasional long trip gets thrown it but not like it used to. Is there any sort of a delete on an 18 or do I just live with it?

[VStar650CL]

Nope, it's a LIN alternator on the gen2's and not PWM. Disconnecting the LIN wire will light the MIL. The only thing you can do is disconnect the battery current sensor. That will throw codes but shouldn't cause any warning lights.

[D1dad]

Is it really a big deal though? I mean it’s been like that for almost 7 model years and never an issue. Although I can see why an agm would be a waste of money and maybe short tripping would cause it to need the tender at least once a month. I did notice that my 40 month old Walmart battery was turning it over a tad slower. Of course it was a 36 month warranty.

[VStar650CL]

Like I said in a different post, if I owned a gen2 with an EFB, I'd be sticking a regular flooded in there the minute the EFB failed. As for how much it matters, we only see recurrent issues on chronic short-trippers and cars that sit a lot. Both are really bad for EFB's, because the dense plates make them much more prone to sulfate bridging.

[D1dad]

Ok vstar, I trust you. I just went to the local farm store and bought a couple of deka gold, regular old flooded batteries. One for the 18 rogue and 1 for my 21 Altima. I know the rogue can use a flooded since that’s what’s been in there for the last almost 40 months. The 21? I hope they didn’t change something with the charging system that would be better served with an agm?

[VStar650CL]

Nope, the system in the gen6 Alties is pretty much identical to the late gen2 Rogues. The '14 Rogues were actually the "guinea pig" for the LIN alternator setup, and in '17 they went to that goofy configuration shared by the grille shutter. That's the setup your Altie has (shared with practically everything else Nissan these days).

[D1dad]

So I can assume that our 24 shares the same setup and I can just use a flooded battery next time?

[VStar650CL]

Yep.

[anarky321]

i have the same question - alternator cycling between 12.0ish and 14.5.....but also setting a current sensor code

how do you even diagnose a bad alternator if the computer normally cycles it that much...i dont think ive seen that on other cars

when i first saw that i assumed the voltage regulator was going out on the alt

im going to replace the current sensor just in case though (since it set a code)

[D1dad]

Vstar? Will the larger group 47 fit in place of the current group 35 that’s in it? I bought an odyssey for an insanely good price and can put the brand new deka I just put in the rogue in my 09 Altima that I gave to my daughter. It’s to dang cold out to go measuring things right now or I wouldn’t be asking.

[VStar650CL]

Size wise, group 47's and 35's will generally fit in the same hole. I can't give you a definite answer, but I'd say it's very likely.