To verify total battery capacity requires equipment equal to that found in electrical testing labs. Common chargers can only provide data for measured voltage, milliAmps in and milliAmps out. If equipped with the feature some chargers can also provide resistance in milliOhms.
Unless we choose to destroy a battery in destructive testing we have to trust battery manufacturers when they provide us information referencing total capacities. If we were to fully discharge a fully charged battery to assess milliAmps out the act would, in one manner or another, ruin the battery forever. Making that even more difficult, most chargers have a discharge cut off level that would prevent total discharge.
The policy of “trusting” the manufacturers has caused more than a little aggravation in the past with Yuneec branded batteries as they admittedly labeled Q-500/Chroma batteries as 5400mA when in fact they were 630A capacity. Yuneec branded batteries for the Typhoon H 480 are labeled as 5400mA capacity but provide pretty much the same flight time as 6300mA battery under identical conditions.
Short version; your battery will only tell you what you took out or put in when an action is performed on the charger.