Check the date of the Left battery (probably stamped on the battery post). The Left one is not the starter cranking one, but it does control the starting system computer. If it's over 5 years old it's due for replacement. A re-charge might help short-term.
Also, make sure the floor under the carpet on the LH front side is dry. If it's wet it damages the starting electronics on the floor. You'll have to feel underneath - there's a waterproof layer that can leave the carpet dry on top and wet about 4 inches underneath.
Do you have a VW scanner (VAG-COM/VCDS)? Not the normal OBD2 one.