Checking out 12v battery condition

Last week I went to start my 2015 Prius C, 50k miles (bought it new) and many, if not all, of the dash lights came on and car did not start. Soon after, a whining sound accompanied by clicking sounds was that were audible even though the key was out.. I jumped it and brought it to the shop I go to here. They replaced the 12v battery which was 6 years old with a S34B20R Platm AGM DHGMP (don't know what DHGMP means). I start the car every day here in the north, but there might of been a time or two when I left the lights on and I had to jump it once before because of that. I’m thinking 6 years on the same 12v is not bad but I have this nagging thought that maybe I have a parasitic draw due to subwoofer/speakers I had installed shortly after I bought the car..or maybe from any other source, however I have no other after market accessories installed. Is there way to check for this with a multimeter under the hood and also to check the charge of the battery using a multimeter, as well as by the on board display. I am not electrically inclined. Thanks.