Hi,
I just bought a CRV 2003 and the alternator is over charging on highway (high revs) but ok in city (low revs).
If it is the regulator, can an external regulator be installed?

 

What voltages are you seeing? Sounds like the ELD is doing what it should.

 

If theres an alternator issue, just replace it .
What makes you think its overcharging?

 

The battery warning light comes on in the dash on highway. Sometimes stays on, other times blinking.
Yesterday I reved up the engine in parked position and battery warning light came on.
After killing the engine, battery voltage showed 12.9 v. and went back slowly to 12.6 v. after a while.

 

I checked the battery voltage after killing the engine. 12.9 v.

 

12.9 is perfectly acceptable. Need to get a voltage while the engine is running.

 

I would start with putting a voltmeter to work on the alternator. What actually is the output voltage at idle, and also at 2000 to 2500 rpm? It should remain at around 14.7 volts approximately. The batt light will illuminate if there is low or no charge from the alternator or if there are dead cells in a battery ( sometimes). Your battery voltage looks ok. I would suspect a failing alternator. They are not expensive and not difficult to replace.

 

$300 for an OEM alternator is not super cheap. The aftermarket stuff is complete garbage. If budget is tight find a second hand alternator from a wrecking yard or similar.

 

My experience with aftermarket stuff is that I have purchased alternators, starters and AC compressors from amazon and Rock Auto for 6 Crvs and I have yet to have one go bad. Honda dosen't make these parts, they are made for them. General quality of off brand ( ie not denso or Hitachi) is pretty good.

 

For reference, on Rock Auto, a brand new AC Delco altenator is $184 and a reman Denso is $150 ( USD)
The load detector and regulator are also availble if you wish to rebuild yours.

 

Always test your alternator output with no loads, and then test it again heavily loaded (i.e. high beams on, seat heaters if you've got them, rear window defroster, HVAC fan running, radio). A failing alternator can sometimes keep up with base load just fine, but starts to flag under demand.