BTW - It's not just battery charge and health that matters. Battery cables and terminals/connections matter just as much. They need to be in good condition, clean, and tight. Next is condition/health of alternator and starter.
Sometimes problems with those other things are misdiagnosed as battery problems and/or cause battery problems.
Recently a starter problem killed the battery in my neighbor's Honda CRV. The battery failed a load test. After replacing battery it still wouldn't start. The starter failed testing and was replaced. Now it starts fine.
In hindsight, the dying starter killed the battery. There was advanced warning, but my neighor is tight for money and has no car knowlege. So she ignored the signs until too late.
Same thing happened with my Buick years earlier.
I always suspect and test battery first. Sometimes a bad battery is the only cause of trouble. Often a bad battery is a symptom of another,
underlying problem.
Sometimes a flooded battery needs distilled water added to it. So check water level
if it's a flooded battery with removeable cap(s) on the cells. For that type of battery, you should check water level once a year.
Sometimes a battery just needs a smart trickle charger/maintainer put on it. But check water level first (for those batteries that water level can be checked).
The next thing I suspect/inspect is battery cables. Cables are easily visually inspected and then cleaned, tightened, and sealed.
Next test the starter.
Next test the alternator.
At some point in the process (maybe last?) test/check the ignition switch electrical parts. Sometimes it's the problem.
Those ^ are in order from most to least likely to cause problems (in my amateur DIY opinion).
Just realized that sometimes it's two problems, maybe more. More than one thing can be true at the same time. Often bad battery cables, starter, and/or alternator can cause battery problems or vice versa.
