1998 Subaru Outback 2.5 won't charge at Idle

[woot422]

New here and after reading a little bit seems you guys might be able to help me out. I have a 1998 Subaru Legacy Outback Limited . We went on a trip back in april and made it to the town we were going to . The next day the car had a dead battery and to me the alternator seemed very hot , so I went to an autoparts store and they tested the alternator on their machine and in the car and it tested good , I bought a new battery 2 weeks prior to the trip also . So being worried I purchased a new alternator anyways and charged the battery before starting up the car after new alternator was in. I also disconnected the wifes amp and sub to make sure it wasn't gonna be a problem and still to this day the amp(500 watt) and sub is disconnected and never hooked up again. Well we made it back home (600 miles) had no problems. Few days later same problem , car died going down the road , I jumped it being that wife was only block away from home and had her drive it home , I charged it and still would mess up . My stepfather owns a shop so I brought it there . He went through it and said that he thinks the alternator was working just not producing enough amperage so I purchased another Alternator from Advanced Auto Parts this time . In the shop it seemed fixed , staying 13.6-14.2 . We also checked all grounds. I cleaned ever ground strap terminal etc . Checked for shorts on wiring , can't find nothing wrong . Well thinking it was fixed it wasn't . So I hooked up a digital volt gauge and used shop gauges . When driving it charges from 13.3 to 14.2 with np's , but when at idle It will not charge , so when we pull up to fast food places , banks , walgreens etc we have to shut the car off or the battery will just go dead . Again I have the stereo disconnected and completely out of the car and dont plan on using it . my dad now said it could be the pulley ? and to get a smaller pully, he thinks maybe the 2 alternators I aquired from the parts stores might of had bigger pully's ? If anyone could help me with this it would be a life saver , I purchased this car for the wife for her bday present and already had to redo the heads so the wife had to wait a few weeks for that and now I can't figure this problem out . I just want her to be safe and enjoy her car. , Again it will charge while driving , just not at idle . Idle rpm seems to be normal . I just don't get it

[plain OM]

When you say it won't charge when the engine is idling, what is the voltage across the battery posts at that time? Also, what is the voltage between the heavy alternator charge post and the battery negative post?

Is the Charge warning light working properly? When you turn the ignition key to ON, does the warning light in the instrument panel light up, and then go out when the engine is started?

And if the warning light does work properly, does it come on when the engine is idling, or is it still off when it appears the alternator is not charging?

I wouldn't discount the possibility that the "new" battery is defective.

[DavidPeab]

I agree with plain OM. The alternator does not "charge" the battery until it senses a need for a little extra juice. So, technically idling with the stereo reconnected, the A/C, and headlights on would actually be better than not running anything. Then the alt would kick in and send current to the battery. It does sound like the new battery has defective cells and is not holding a charge.

[woot422]

Well I took out a battery from another car and put it into the wife's car and sure enough the battery I purchased from advanced was bad . I let it run for hour and half and it would hang around at 12.6 ish with heated seats on , lights on brights , radio (not with amp) , heater blower, and watched it when the radiator fans turned on , when the fans were also on it would drop sometimes to 12.3 ish but then alternator would kick in and put it back to 12.6. I turned everything off and it stayed around 14 idling also . So I wanna thank you for helping me diagnose the problem . Well at least I have an extra alternator now lol . can't beileve they sold me a bunk battery , they tested it and said it checked out good , hopefully they return it . They will prolly tell me oh it tests good , and refuse to replace it , I can see this happening . Again thank you so much , this not charging headache is gone and now the wife will be able to enjoy her radio again and not having to shut the car off when she stops at places lol