My 2008 Jetta SE 2.5L has the battery as follows: ENERTEC EMC // 1J0 915 105 AD // 12V 61 Ah 330A DIN // 540A EN/SAE.
It would appear that the battery can no longer hold the starting charge after an unfortunate incident of having the battery drained up (with the engine being off), and now it seems like it basically can only hold the surface charge, even though it was running just fine prior to the aforementioned discharge.
The top of my battery (including the six caps) looks exactly the same as the one featured at Should i check quantity of battery liquid?, except that mine also has an eye between the terminals and the caps themselves are beneath a sticker.
How many ml's of distilled water would it be safe to add to the battery, without risking creating any more problems?
I've opened up two of the six caps so far, and I couldn't see any plates, so, I'm not exactly sure if I can or cannot add more water to it. I've owned the car all along, and I'm pretty certain that no water has yet been added in the 6 years the car had the battery.
UPDATE: I've added 2x 10ml syringe shots into each cell (I got the free oral-use-only syringe from Walmart Pharmacy for free; I got distilled water for small appliances from Target); that's a total of 6x 20ml = 120ml of H2O. It seems small enough to not cause any leaks; not sure if it's large enough to make it hold a charge sufficient for the start motor. And, just to be clear -- the discharge was only enough to stop powering the starter; the battery has not been fully discharged (to not power anything at all) in the last year; it has only been fully discharged (through a lightbulb) once, about two years ago. Right now, prior to adding this water, the battery simply stopped holding a charge to power the motors -- it is still holding a good charge for the electronics and power locks etc. I hope this extra 120ml of distilled water would help revive it without any ill effects. BTW, it does have a min/max marker on the side, however, it's not really visible, due to the battery being wrapped up in some special blanket.