Battery dead?

[G Men 08]

Three days ago I was using vagcom to change codes for a few convenience features. Maybe half hour to 45 minutes. It killed the battery, so I charged it over night.

Fired right up that morning for work. After work I go out and torn the key, slow cranks and then fits right up. Voltage output reads 14 according to the dash gauge.

Check cables, negative cable is corroded at battery terminal so I replace that and put it back on the charger for about 8 hours. Take it off of the charger (charger reads full charge) did some random non car related things for a few minutes and come back to move the car, turn key to check voltage, it's at 10ish. Cranks slow, but fires right up and reads 14 volts on the gauge.

What can I check via vagcom to pinpoint that it's the battery?

What battery do you recommend?

- - - Updated - - -

I have been removing the terminals every time I charge. Is that necessary?

[Sparkstack]

If your multimeter has a range function, clamp it to the battery and then start the car. See what the minimum voltage is when cranking. Anything below 9v on a supposedly fully charged battery means time for a new one.