I recently had some issues similar to yours and it ended up being my alternator.
To test it you will also need that 'round-to-it' multi-meter...
With the car running, test it at your battery terminals and the result should be 13-14v, if I remember correctly. I can't remember if I removed the ground or not but if you do a search on the forum you can find out the proper procedure to do the test.
Mine was putting out 11v which told me it was not generating enough power to charge my battery and help run the car's auxiliaries. Once I changed my alternator the problem went away.