Shipo, my issue maybe somewhat similar. Except for the one day it wouldn't start, it has now been starting fine every time. Based on your post, I didn't hasten to replace the battery. I did try some other electrical tests with the multimeter. I found out that the 2 terminals inside the engine compartment fuse and relay box as well as the B+ terminal of the alternator measure 12+ volts. However, I got random readings between the battery positive terminal and the alternator case, which is supposed to be grounded. Perhaps it is because the case outer skin is weathered and may not be a good conductor, see attached pic. I couldn't verify the voltage at the terminal on the starter solenoid because I'm not sure where it is located or how to reach it. What I will say in terms of symptoms is that on the occasion when the engine wouldn't start, I did hear a growl upon turning the ignition key and then silence.