Got the bike last week, and it started up and ran great. But it would only run for 20-25 minutes before the bike would just start sputtering and then stall out. When I tried starting it again, it wouldnt start until the battery was recharged. We got the battery checked at auto zone, and they said it was fine.

I went to the local cycle shop, and I was told it had most like the alternator was draining the battery of its charge. Now, the guy didnt actually call it an alternator, but he said it could be one or both of two parts thats not working right and I forgot what he said. So how would I go about trouble shooting which part needs to be replaced?

Do you have a voltmeter?

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2008 Ducati Hypermotard 1100
2006 Kawasaki KLX250S
2004 Honda CBR600RR
2002 BMW R1150R
1996 Ducati 900SS

Yeah, I have a volt meter. Earlier today, I put the freshly charged battery into the bike and then started it and let it warm up. Then I used the volt meter and it it said 12.3 v. Took it around the block a couple times, then measured it again and it was down to 11.4. Then I rode it around a couple times, and then when I checked again it was at 6.8 v. At that point, I shut off the bike and it wouldnt even crank when I tried to start it up again.

How old's that battery? And has the battery ever been run down before?

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2005 Triumph Bonneville
2005 Suzuki V-Strom 1000
2003 Triumph Trophy 1200
2009 BMW F650GS (wife's)
1990 HD Sportster XL883 (for sale; wanna buy a Sportster??)

It sounds like your charging system, not necessarily the battery itself. The battery voltage with the bike running at 2000+ rpm should be about 13.5 - 14.5 volts.

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'80 Suzuki GS550L

pchast is right, get the bike running and put your voltmeter on the battery. When it's around 5000 RPM it should be pushing around 14.5 Volts into the battery.
If it isn't putting out that kind of voltage you need to check two parts. First is your generator. Second is your regulator/rectifier. Test the output into the battery first and let us know, we'll go from there.

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Have owned - 2001 Suzuki Volusia
Current bike - 2005 Kawasaki Z750S
MMI Graduation date January 9th, 2009. Factory Certifications in Suzuki and Yamaha

Great advice above, couldn't suggest better.

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UJust put a freshly charge battery in the bike,started it and set the enrichener to 5k. The volt meter was reading 12.5 v. I'm not sure if the battery has ever been rum down or how old it is.

The battery isn't charging. You need to check your rectifier, regulator, and your stator. If your not sure how now is a good time to get a service manual.

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Always wear a helmet, eye protection, and protective clothing. Never ride under the influence of drugs or alcohol.

Yup, JohnJ has it there. I'd test your stator first. Your regulator and rectifier are both in one piece, but usually when they go bad they go WFO.

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Have owned - 2001 Suzuki Volusia
Current bike - 2005 Kawasaki Z750S
MMI Graduation date January 9th, 2009. Factory Certifications in Suzuki and Yamaha