My battery light turned on in the burnout box tonight at the track.
It only turns on at high rpm and the voltage started dropping to about 13.3volts before I let off.

Now the car drives lean at cruising and partial throttle but the voltage is steady at 14.1-14.2 while cruising.

Could this be the battery or alternator?
The alternator is less then 1 year old brand new bosch.
The battery is a shuriken bt-20 and I didn't have any problems with it in the past.

The motor is a h22 sleeved, 12:1, skunk2 pro2, twm itb, hondata s300.

 

Get them both tested or test them.

 

Belt may be slipping.

 

I checked the belt as well as a couple other certified mechanics.
Checked the grounds as well.
Checked the fuse and it's not blown.

 

Then have the alternator tested.

 

Its most likely the alternator... Seen this on a few friends cars. If you cant hear the belt slip, then its gonna be the alt.

 

i've had this happen before. even seen a blinking battery light at high rpm.

ultimately the same alternators **** the bed, not always immediately, but eventually nonetheless.

i believe it's something in the regulator or the aftermarket winding that enables them to over-charge at high rpm and eventually leads to them burning up. but i'd never dry-rev an engine to 9k just to test a hypothesis concerning a reman alternator. (yes i read that yours is a 'brand new' bosch) i can also think of a few reasons why this wouldn't be true. but like i said, they always ended up crapping out with time.

and don't get me started on aftermarket starters and alternators.. reman or 'new..' getting one out of either that'll last a few years is always a crap shoot.

 

i switched the alternator with another one and the car is still not running properly.
I have not revved it up to when the battery light turns on yet because the car is running lean randomly.
It would just misfire and this started when I left the track a couple nights ago.
I checked all the plugs and they all look good. Ill have to check out the battery.
Could a battery cause the battery light to turn on at high rpm?

 

Yes... I have seen vibrations from engines(solid mounts) cause battery plates to shift and touch together.

 

I just had this same exact problem, took us 5 months to figure the issue out. Is your battery in the trunk (mine is), I had to replace the wire the runs from altenator to the battery kill switch in rear (it was too small) also my battery was bad. The car went from holding at best a 13.6-13.8 at idle to 14.0 at idle and 13.9-14.0@WOT according to dyno logs.

 

I have a shuriken bt20 battery and it's in the front.

Also all the battery cables/grounds are new.

I'll try a new battery.
Would there be any problems running 2 different batteries? I want to add one in the trunk and remove it for the track.

 

Do a load test on the battery..
Attach leads to the battery and crank the engine. If the voltage drops more than 2 volts the battery is going bad. If not look into the wiring from the ecu to the alternator.
12v signal constant with key on
Signal ground from ecu
And signal voltage from ecu.
Check continuityfrom the harness plug and at the ecu side of the harness.
If the alternator is putting out 13 volts it should be fine unless your getting high voltage spikes.