The different values are little so not a problem.its a real sky rc one but when i hold dec and enter when powerd on just says system update please wait so not like the copy's that go to a cal screen?
i think i need a new multi meter as that was like 10 quid in a kit 15 years ago and prob out more than the charger.
Remember batteries are chemistry and not physics.
A calibrated device does not mean it is perfect but that it is within a window, 5% is good for any device.
Most modern electronic devices are close enough to not matter, when you had a moving coil meter that had been dropped a few times then that was different.
I would stop worrying about discharging your batteries and charge them and use them, has the new photon displacement ray arrived or have the Americans held it's import up?