Battery drain I disconnect the positive battery post and still have battery drain

Disconnect one battery lead and measure parasitic current draw with DVM set to 10amp range and test leads connected in series with disconnected battery cable and battery post. With ignition in the off position and vehicle doors closed. Remove fueses one at time to isolate circuit which is drawing current from battery.

You have something drawing on your battery. disconnect the nevagative cable. hook a test light between the negative cable and negative battery post and pull fuses till the test light goes out. when the test light goes out you've found the circuit that's drawing down your battery. trace the circuit and look for a short to ground or if something on that circuit is staying on.

How you check a drain. First you will always have a drain if you have a clock in the dash or in your radio. It will be small. Disconnect the positive battery cable and put a test light in line. Watch the light and start pulling fuses when the go's out you will know what to look at for the draw

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The alternator may charge fine but could drain the battery through a bad diode,have you checked the alt for a bad diode?Disconnect the battery positive cable.Put a regular 12v test light between the battery positive post and the positive battery cable.If the test light is bright you do have a drain,if dim it is OK.A dim light may mean the drain is internal in the battery.If you do have a bright light remove a fuse ,one at a time from the fuse box until the light goes dim.Once dim you have identified the bad circuit.If removing all fuses do not dim the light,disconnect the alt charging wire at the alt,if that dims the light,then you do have a bad diode.DO NOT create a drain(bright light) when checking for the drain by turning on the key or opening a door/trunk etc.
Also,do an overnight battery check by disconnecting the battery overnight,if things are fine the next morning after the battery was disconnected then it is a drain in the vehicle,if the battery is dead even after being disconnected overnight,,then the battery is bad.

FIRST THING, START THE TRUCK, PLACE A VOLTMETER ON THE BATTERY. VOLTAGE SHOULD READ BETWEEN 13.90 & 14.80. IF THAT IS OK, THERE MUST BE A BATTERY DRAIN. TO CHECK FOR A BATTERY DRAIN, TURN OFF ALL SWITCHES, CLOSE GLOVE COMPARTMENT, MAKE SURE THE LIGHT IN THERE IS GOING OUT. OPEN THE HOOD, CLOSE ALL OF THE DOORS, MAKE SURE ALL OF THE COURTESY LIGHTS ARE GOING OUT.DISCONNECT THE NEG. BATTERY CABLE. CONNECT ONE END OF A 12 VOLT TEST LIGHT TO THE NEG. POST OF THE BATTERY. FASTEN THE OTHER END TO A METAL PART OF THE MOTOR. IF THE LIGHT COMES ON THERE IS A BATTERY DRAIN. NO LIGHT, NO DRAIN. IF THE LIGHT IS ON, YOU NEED TO UNPLUG THE FUSIBLE LINKS FROM THE POSITIVE CABLE ONE AT A TIME TO ISOLATE THE DRAIN. ALSO, DISCONNECT THE ALTERNATOR, & SEE IF THE TEST LIGHT GOES OUT.BAD ALTERNATORS CAN CHARGE THE BATTERY WHEN RUNNING, & DRAIN THE BATTERY WHEN STOPPED.

You basically said it. Something is probably draining the system. Disconnect the positive lead off the battery and then connect a amp meter in between that lead and the positive post and check the reading. If your over 100 milliamps you have something drawing power somewhere.

Pull the positive cable off battery. Put a test light between the battery post and the positive cable. If there is a light you know it is draining the battery. Now pull fuses one at a time until the light goes out then you will know where the problem is. To save time make sure you glove compartment light is going off and check you trunk light.

The new alternator may have a closed regulator draining the battery,put a volt meter,or test light in line with the ground cable,remove the ground cable,and put the test light clip on the ground cable,and the tip of the test light to the negative battery post,or contact,it does not have a post,If it lights the test light,and it does not fade off,then there is a draw,unplug the alternator regulator plug,see if that turns the test light off,if it does,then the alternator is defective,then if need to continue testing,remove the interior light fuse,completly,and then pull one fuse at a time,to see if the test light goes off,when it does,that is the circuit that is drawing the battery down.The clocks will pull to many amps sometimes and cause this also,be sure to disconnect the battery over night to make sure the battery is good also,so you wont be doing all this for nothing,and you may want to have the battery load tested.

Use a 12volt test light between the positive battery post and the positive cable with the positive cable disconnected from the battery.
Keep key off.
You will see the test light "light" with any drain.

Any drain showing a dim test light is..... OK
Any drain showing a bright light is.....BAD

Disconnect items (fuses) one at a time and watch the light.
Keep the doors closed....the inside dome light is a drain with the door open!
After fuses are checked....disconnect the alt if needed and watch the light.
Keep going until you get rid of the bright light.

No, corrosion will not cause a battery to drain, even if the corrosion is on the terminals. Several factors can cause battery drain, I would first have the battery tested to see if the battery it self is not bad. If the battery is good, then the most common is a short. All most all new cars have a certain amount of drain,(measured in milivolts) this drain is for clocks and computer memory's, and it would take several days of a vehicle sitting for the battery to be drained. Don't immediately assume you have a problem if you see 2-6 milivolts of drain on a battery with the key out, now if your battery is being drained after being parked over night, you have a problem. The easiest way to pin down the problem short is to disconnect your positive battery cable from the battery, take a 12 volt test light and clamp one end to the positive cable, and hold the probe to the positive post. Now if you have a short the light will come on. Have someone help you by pulling the fuses one at a time. If when a fuse is pulled the light goes out you have isolated the short to that system. If you pulled all the fuses and the light never went out try disconnecting all the wires from the alternator, 9 times outta 10 do this will let you know where your short is. If the system is not critical like power locks some people just leave the fuse out.