Alright ill start off with a little description of the problem, and then state what Ive attempted to do to solve the issue. For a while now, Ive noticed my car being a little hard at starting, but i didn't really notice until this whole problem started.

I left my key on in my car while i was cleaning it out or something. Went to start it and the battery lost its juice. I kinda thought it was strange considering it never had this issue before. Anyways, threw a battery in it and it seemed as the problem was solved. Fast forward a week and i started getting the same hard starting. So tested the alternator and it was only reading apx. 12.5 volts at idle and did not increase when i revved it up or drove it. Replaced the alternator with 2 other units known to be good and i still have the same exact problem. The voltage is the same at the alternator, both wires to and from the fuse box, battery, and ignition switch.

What i have tried:
-Through hondata, i disabled both the ELD and the alternator control. Neither did anything.
-Every fuse in the entire car is good.
-Added a ground to the engine, and checked all old grounds
-bottom alt bolt (ground) is tight
-all fuse box plugs are there and intact
-i pulled both the charging wires out and inspected them
-battery light DOES come on when the key is turned to on

I'll update when else i try as i go along. Feel free to ask questions

 

bump

 

Have the alternator tested at like autozone or advance auto.
If thats good, and you have a new battery, that rules those both out.
Maybe its the ECU not telling the alternator to charge?
Can you try and swap the ECU for a quick second?

The car runs fine? It doesnt die or anything?
The alternator must be charging if the car never dies..
Maybe you have corrosion on the alternator output terminal or wire?

 

3 different alternators have been tested that came out of tested and running cars. That is ruled out for sure. New battery. As for the ecu, the next step it to trace my alt control wire but i can disable the alt if i want being that i have S300. As far as dying, not really but, if i dont charge the battery and i just try to flip on my headlights and roll they dont come on(hid's). And if i just start it up with a jump box, i couldnt use most of the accessories at once or it does die(no radio/heat/headlights/foglights at the same time) unless i charge the battery or it has been running for some time.

The actual charging wires/terminals have all been checked/tested