Have you done a test at the battery for voltage, running? You should read running, 13.6 or better (approx). If you are getting this reading then your alternator is putting out the correct voltage to keep your battery fully charged with the lights on. If your lights go dim when engaged, and the alternator is new, then your battery isn't storing the energy correctly. Most likely a bad cell or plates.
I've never seen a battery fail the hydrometer and pass a full load test. If you have another battery to try, I'd put that in there and try it out. I'll be willing be bet that the internals of the battery are bad.
Keep us posted.
im looking for some help with my 1999 F150 4.6L 4x4
after frying a 130amp ALT. I decided to come here. This is the deal
All accessories/guages died amid a drive but still ran, made it to a garage where it eventually stalled/died at idle.
Battery was charged, failed a hydrometer test got to the parts store to be tested apparently debunking the hydro test and passing THEIR test with 100% charge.
Install new 130amp ALT, it was shown to me to be holding power to the battery just fine, but when I was asked to turn on the lights, the battery then began to slowly drain unless I had the engine revving real high.
My Theory is a possible bad/not strong enough connection somewhere in there did not allow the battery to charge properly, thus overworking the alternator and frying it.
I was told that it could possibly be a faulty wire connection running from the ALT to the battery and apparently this also included wiring to the starter as its all connected, I was also told it could be the "fusible link" cable which I can and only could get direct from FORD only.
Any input would be much appreciated.