That one got me also. Wifeys Subaru 5 year old battery in five year old vehicle, replaced about six months ago, when pulling it to be replaced noticed the star shaped threaded filler caps and line in translucent case for proper level. I did not feel so bad as the dealer has done ALL maintenance which come with fluid checks.
Glad this AM I changed the battery last Aug/Sept as we have -14 F and -27 wind chills at 7:30 cranked and fired pretty well considering.