Alternator. How to check.
 

Hello.
I need to check my Alternator. I know it charges the Baterry, but i think it do not do it properly.
When i change the baterry it crank fine, but few days after it do not crank as well. I change the baterry because the cranking was awfull and when i need to crank the car with another batery it goes perfect.

I change the baterry and it goes perfect, but in 2 or 3 days, was the same.

The voltage with the car off is 12.2 and with the car running is 14.2
I think maybe the estabilized or the charging circuit is bad. Is posible i could check them easy?

The car is a mk1 1.6 JRSC@8 psi.

Thanks.

Sure sounds like alternator. Also check to make sure you don't have any corrosion on the battery post connectors or at the alternator.

If you were in the U.S. I would advise you to go to Autozone (auto-parts store) to have them run a diagnostic on the alternator (which they can do with the alternator still on the car).

Do you have any similar stores in your part of the world?

Edit: After re-reading your post, it sounds like you might have a parasitic drain on your battery.
Use this method to check:
http://www.wikihow.com/Find-a-Parasitic-Battery-Drain

Something in the car drains the battery. Remove the ground wire from the battery next time you park overnight, and next morning, reconnect it and see if it is ok.

If when running the voltage is 14.2, the alternator sounds fine.

Ditto what Reverant said. Disconnect the battery when you leave the car for a long time.

And you only need to disconnect one terminal:facepalm: