If you want to learn more about batteries, a good place to start is: https://batteryuniversity.com/
Bookmark it, and read the section you are interested in. If you know nothing, expect to have to read it a bunch, play around with the batteries and charger, and read some more. There’s a lot to learn and you won’t get it overnight. This forum is full of accomplished battery geeks.
The LaCross is a fine charger. I have a lower end unit I use a lot, especially for AAA since it has the 200mA as starting charge.
If you don’t understand the manual at this point you might watch some videos: La Crosse Technology BC1000 Alpha Power Battery Charger Review - YouTube
There are a lot out there.
I looked up the Corun website. They have a BUNCH of battery types.
I couldn’t find individual cells for sale, just small packs.
Nominal voltage for ALL NiMh is ~ 1.2v. A way to think about this is ‘middle working voltage’.
LSD should keep most of it’s capacity for a loooong time (many months). Non-LSD STILL should keep voltage for many weeks to a few months. If they lose voltage really quickly (days to a couple weeks), they are junk.
You can do a ‘refresh’, but with new cells that should not be necessary and takes a long time (days). Personally I’d do a ‘charge test’, which will charge>discharge to ~1.0v>recharge >> then tell you the discharge capacity. For AAA I’d use 200mA. For AA 500-700mA,
Once charged they should show about 1.4v+, BUT only for a day or 2. Then settle down to 1.3Xv and STAY there for a long time. If they don’t, then there is something wrong with them.
IMO, barring some actual defective hardware, I’d say the ‘software/you’ is still on a steep learning curve. You are doing something wrong, or not understanding what you are doing…yet. Hang in there, you’ll get it.
Note - have a REALLY smart buddy. Programmed software for a living. Excellent mechanic. Writes and sells programs for Android phones.
After a couple years of me working with him he’s only now starting to get the basics. Like a lot of people, I think the real problem is not really caring to put much effort into it.