The Nitecore USB battery chargers, especially the QC wide dual charger, do some strange things with the battery reset point. In some cases the battery does not charge completely and in others is does, but the chip reads less.So I have an a6000 and looking for an external charger. Is the BCQM1 the best option if I want fastest charge times (FW50 batteries) and not too concerned about charger size?
I see some third party options like Nitecore which has a very cheap dual battery USB powered charger but reports are it usually taps out below 90% state of charge.
The dual sided Nitecore chargers only charge one at a time, alternating as the display alternates. I tend to have one of those on the carry-on and one Canon OEM in each piece of checked luggage.
I have some generic USB dual charger for Sony, but it is not fast. In general I'm not a fan of fast charging. Ideally you will have plenty of batteries. Any OEM charger should be fine of course.