Capacity is the leading health indicator of a battery, but estimating it on the fly is complex. The traditional charge/discharge/charge cycle is still the most dependable method to measure battery capacity. While portable batteries can be cycled relatively quickly, a full cycle on large lead acid batteries is not practical for capacity measurement.
Lithium-ion batteries have revolutionized the way we power our lives. These advanced rechargeable batteries have become integral to countless applications, from portable electronics to electric vehicles and renewable energy storage.
For info: I've been measuring lithium ion cells with 100mA constant current and 3.5 minimum shutoff voltage. Found the general, inexpensive 14500 cells stamped with 4000 mAhr show about 150 to 325 MaH capacity. The larger 16850 also stamped 4000 mAh show about 1000 to 1600 mAh capacity.
These advanced rechargeable batteries have become integral to countless applications, from portable electronics to electric vehicles and renewable energy storage. In the dynamic landscape of lithium-ion battery manufacturing, a suite of cutting-edge tools has emerged to facilitate both production and rigorous testing.
To charge the battery I use a simple usb cable, but with a device that measures voltage, current, time, and total milliAmp-hours. These gadgets can be found on the internet and are cheap. So, to determine the capacity of the Li-Ion battery at hand, just let it die down and recharge it.
I.e. is there some device / method that given a a Lithium-ion battery which is supposedly fully charged determines: Lithium ion batteries when sold should show a 60% charge if they have been properly stored. When storing lithium-ion batteries yourself you should discharge to 60% and keep in a freezer.