I now always use my meter when charging.
Make sure the device is actually charging – sometimes it appears to be charging but it’s not actually drawing any current
If a device, for example, draws 0.4 amps when it starts charging, when it gets down to 0.1 amps I’ll disconnect it. Otherwise, it will continue to trickle charge, using up my USB power bank, but the added charge is minimal. Not a big effect though.
Also, if you only charge a lithium battery to 80% or 90% the battery will have a longer lifetime. This will be when the charge current drops from, for example, 0.4 amp to 0.1 amp. Over time, the battery gradually loses capacity. This problem is reduced if you only charge to 80% or 90%. Rex mentioned this.