Hello, new to the forums.
I've a 2008 Civic EX. Red battery indicator lamp came on while driving the other day.
Lamp extinguished on next drive and didn't reappear the next time I drove.
A day later it was occurring every drive. Checked voltage at battery with a multimeter with car running & not running. Only showing battery voltage. Same when measured at P+ lug on Alternator.
I was 95% sure it was time for a replacement alternator. Sourced a Carquest one from Advance Auto.
Decided to remove alt & batt and take BOTH up to store (in a different vehicle, obviously) to get bench tested - I wanted to be sure it wasn't the battery (though I thought that unlikely).
Old alternator failed bench test. Battery passed test, with low voltage. Test unit put a charge on it while I waited.
Got home & installed new alternator along with new Gates serp belt. (I figured while I'm in there, I may as well have the fun of routing a new belt!)
Get it all put back together. Double checked connections. Did new battery hold-downs, (old ones seized with rust), felt washers, clamp bolts, shined up lead terminals, used battery terminal spray, the works.
Check batt voltage before cranking her up. After cranking, alternator is putting out 13.8 - 13.9 measured at the battery posts. Great! It's sorted.

This was 2 days ago. Didn't drive yesterday. Went to the store today. On the way back, got the dreaded red battery lamp again! How?
Get home and throw the m/m on it - and sure enough, only reading battery voltage! Alt isn't charging. What is going on.

I'm at a loss. Appreciate any & all help.
Regards

 

I figured I'd post an update on the off chance it might help someone else;

Turns out the replacement alternator from the parts store was bad. It died in 2 days (or less).

Sourced a Bosch unit from RockAuto. Once it came in, I installed it.

Everything's working like a champ. Moral of the story: don't assume a new alternator can't be bad (nearly) out of the box, and don't give up.

 

You have learned a valuable lesson here: Local auto parts store electronics are of substandard quality compared to OE products and installing them almost always ends badly. Genuine OE electronic parts (alternator, starter, distributor, IACV, VTEC assembly, etc.) are expensive but worth it... and if you can find the SAME branded product from an aftermarket source, saving some $$$ isn't bad either.