Charging system issue: S13 SR20DET

[Seraphim38]

So I just got my car tuned by a great tuner in Portland, but on the dyno the battery went dead and it was run off a jumper box then charger (I think that the jumper cables got reversed by someone). The next day the Odyssey PC925 battery was dead (measured at 10.7V). An overnight charge later (measured at 12.0V), the car starts and runs fine but once running is at 11.8V and drops to 11.6V-11.5V under load (lights, windshield wipers, etc.). So I figure it needs the alternator replaced. I checked the fuse block for the alternator fuse and it appears intact, though I didn't remove it and measure it for resistance.

I swapped the alternator last night for a known-working spare, and got no change. This Odyssey enables me to drive about 10 miles +/- with the wipers and accessories on before I need to charge it again, or at least, I haven't driven it until it died so maybe it will go farther.

So, any ideas on how to fix it?

[Edwin562]

have you tried another battery??? could be batt is dead..

[KiLLeR2001]

Get a real battery. Do you have the alternator connected correctly? Don't forget to ground the back of the alternator to the chassis.

[Seraphim38]

I haven't tried another battery. I assumed that since the voltage was low when the engine was running, and that the battery seemed to sustain engine operation for a drive, that it was ok.

[Seraphim38]

Battery tested out fine. charged to 14+ volts and was load tested by the shop next to my work.

I am going to remove the alternator and take it to a shop to have it tested. Maybe the spare 'good' alternator I got wasn't 'good'.