In the original post it said you had the alternator tested but it didnt say anything about having the battery tested. Have you had the battery tested.
A 2000 SE wagon would have had a likely manufacturing date of late 1999 early 2000. Most quality aftermarket batteries have a 10 year warranty. Its 2013
and OEM batteries usually don't have any warranty. Its sounds like you just need a new battery.
Get your battery tested. Big 3 upgrade is good. But it requires a good battery to be useful.