My battery drains out completely if car is not used for even one day

Could just be a bad battery.

I used to work at an auto parts store, and every once in a while we'd find a brand new battery that simply wouldn't hold a charge.

Had this happen to myself just this past fall. Bought a new battery, within about 3 days, the battery light started coming on. Brought the car back to the service center, and sure enough, they came out and told me the battery would not hold a charge, and needed to be exchanged.

Even a brand new battery does not mean that the battery is good.
Take it back to wherever you got it and have them test it. They can tell you if the battery is any good or not, and whether it's the battery or if it's the alternator.

First you can not test an alternator by disconnecting the battery cable. That is what we did back when cars had generators. Today you can fry the computer and alternator running the engine with the battery cable off.
Meanwhile, I would look for a fuseable link or main fuse problem. The alternator circuit may not be connected to the fuse box and battery.

You need to make sure that your getting good conection to your battery. If your alternator is fine, as you stated, you might not be getting a good conection. Your alternator may be keeping your battery alive just enough when your driving. Check all connections. Hope this helps.

there is an open cirket somwhere draining the battery

you may have a problem with the alternator sometimes not charging,may test okay sometimes, take a good look at the alternator and also make sure nothing is staying on, like inside lights, glove box light or brake lights, keep an eye on these things when parking the car for the day,something may be draining the battery down slowly.

Does the battery charge even after it drains. Even though it's a new alternator, it could still be bad. The battery could even have a dead cell because it's draining while you're driving. Sounds mainly like the alternator output isn't enough. Internal voltage regulator inside the alternator is usually a big problem, it can't be replaced, except by a new alternator or have yous rebuilt.

bad alternator possible or bad battery..even though its new that battery can be bad. I would take a volt meter and with the engine running check the volts of the battery..If the volts are 12 you need to replace alternator, if volts are 14 you need to check the battery. to check the battery hold the volt meter to the battery and have someone start the car..while the starter is cranking battery volts should not drop below 10volts.if they do your battery is bad.

In my case, the instrument cluster was bad, causing the MFI display and radio to go haywire and putting a contstant drain on the battery. $760 to have the VW shop replace it. No problems related to the battery or alternator have occurred since.

Good luck.

[email protected]

The battery will be fine, the alternator might be draining even if it is charging OK, usually it is the alternator (if you can disconnect all the wires to it and see if it still drains.Otherwise it is a big drain, so what is doing it will be getting warm. It might be unwise to use an ammeter to check as the draw would need to be over the usual 20 amp max for most meters, get back to me with what you find.

Even though your alternator charges in the daytime, when there is a load on it, the alternator can't bear the load, your alternator maybe weak but not completely bad. You may have to have your connections checked