Re: Newbie has some questions!
I usually keep a spare AGM around, I usually buy a size that will fit anything and has dual terminals but a friend needed one temporarily (think that means like the temp buildings in DC from WWII).
My experience with AGMs is that they cost more but are likely to outlive me.
I use the DVM trick but modern computer cars have a habit of running a few things for a few minutes before settling down so I connect the DVM initially with a shorting wire between the leads, wait a bit, then remove the shorting strap for a true reading.
Frankly, I never heard of so many battery related issues before this forum, in other cars if they'll crank, they are OK to run.