To fill just carefully pour in some pure water. I have taken a shine to the Prestone radiator and battery water, it is purified and demineralized. Do not fill above the bottom of the neck as it will overflow once it starts charging. You don't want acid running down the battery and all over the tray. You might be able to save the battery, but the life has been severely shortened. When you do replace the battery, be sure to check the water level on a regular basis.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.