New battery, still need jumpstart

1998 Nissan Altima - Had an older battery and needed a jumpstart earlier this week. I replaced the battery and was fine for a few days, now it needed a jumpstart today to get started.

I’ve noticed the AC fan changing speeds here and there over the last couple of weeks… any clue what’s going on?

Check the connections at both ends of the cables first.

The belt may be slipping or the alternator may be failing.

Have the alternator tested. Most auto parts stores will do it free.

 I agree with mcparadise.  Many auto part stores will check the battery and the charging system for you for free while you wait.   If they do the test for you be sure to remember then when you do need to buy something.