Well, that’s one of the many reasons (side from build quality first and foremost, and being able to “resurrect” semi dead cells…) that I bought the Opus BTC-3100.
I wanted to be able to monitor the life of various brands/types over the long haul.
As for what was also suggested with a general purpose DMM, I can’t say that I’d recommend that to the average user. It’s great (and easy, and safe enough) for measuring “raw voltage”, but that’s where it stops IMO. (No disrespect intended to Fenrir) Also worth noting, most cheap meters can’t handle 10 amp+ discharges (not that you’d have to discharge so high, but if one wasn’t versed in designing a safe discharge circuit for such an application…)
To measure battery amperage (current), means you’d have to have it in series, in circuit, with a mod under firing conditions, so you’d almost have to jury rig a test jig of sorts. I can picture all kinds of bad outcomes with that… Never mind the math and calculations for the mah that would follow once the full discharge is complete.
It’s simpler and safer to just buy a charger that can do all that for you.