RustyOldNail
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3.52 showed on my digital Nitecore for one of my older batteries. This was after perhaps 3 loads and then it was depleted. I don’t have a dedicated DMM unless it’s the same as what my Nitecore displays
Using voltage readings is very approximate but gives you another clue. The fact that you’ve noticed fewer bowls means that batteries voltage is getting lower faster as it’s having trouble supplying tha amperage needed. I forget, but believe the “low voltage cutoff” of the TM is 3.3 volts. After a load is removed from a lithium the voltage will go back up a bit, as you have noted after removing it from the TM and then inserting on your digital charger, voltage came back up a bit, but under load this battery can no longer deliver. The better tools for knowing a batteries heath are AC resistant and DC resistance meters, some crude DC ones are built into chargers, but this is beyond most users interest.
However a decent DMM will be a lot more accurate then most voltage readings on inexpensive chargers (a lot due to the spring charger contacts), but a DMM can be useful around the home, continuity testing, reading home AC outlets, etc.