Watch this video.
Parasitic Drain.
It is all about the technique, not the actual repair !
The first important step is at 45 seconds into the video. That first step is to set your multimeter to the 10A setting (there is likely a unique plug on the meter for 10A) and then disconnect ONE battery cable and connect your meter BETWEEN the battery post and that cable.
You have be carful using that method today.
Many if not most modern vehicles will draw more than 10a when the cable is rehooked all the modules turn on and some even the lights turn on for a second or more and blow the internal fuse in the meter.
I made up a set on leads with a fuse holder to use a 7a mini to protect the meter.
This^^
I never watched the video but Im going to assume it involves throwing a meter in series and pulling fuses? Easy enough.....for an old vehicle.
Newer vehicles with modules that will stay awake for a designated amount of time even after the key is turned off, and 'wake up' when power is reconnected take a little different approach.
Here is how I do a parasitic load test on anything newer.
-Open all the doors and use a screwdriver to close the door latches. Disable underhood light.
-Unhook negative batt. cable and use a jumper wire to reconnect negative cable to negative post on battery.
-Let vehicle sit for 60 or so minutes....dont touch anything.
-Set meter on 10 amp setting, hook in series between neg. batt. cable and neg. batt. post. Positive meter lead on neg. batt. cable, neg. meter lead on neg. batt. post.
-Remove jumper wire from second step.
-Check meter reading for excessive draw.
If its excessive then I will do a voltage drop across all the fuses and hopefully find the circuit in question.
If I find a large voltage drop across a fuse (there is a chart for this) only THEN will I pull a fuse to 'double check' on the meter.
Some people will start pulling fuses one by one instead of doing a voltage drop across them, but then when you stick that fuse back on and it wakes up the module it powered, you're back at square one, which is sit there and wait for that module to 'go to sleep' before you can continue testing.
Clear as mud?
As for batteries.....I sell NAPA brand at the shop....partly because of convenience, partly because Ive had good luck with them. They are made by East Penn.