While I have the Nitecore I4v2 charger, and am using it on some Eneloop AAs as i type, I recently got a Thrunite C2.
This is an 18650 battery encased in a nice aluminum tube that will act as a USB supply, or can recharge the provided battery, from a USB source preferable one capable of 1.72 amps.
It can use and recharge other 18650 batteries but 1.72 amps might be a bit much for some 18650's.
I just used it and am recharging it now and it is only recharging at 1.22 amps, not sure why.
Amyway, if one wants a 2 bay 18650 charger, well that implies small size desirability. The C2 is not uch larger than an 18650 and can act as both a 18650 battery charger and a USB power supply when the battery is charged.
I'll not be travelling with my Nitecore I4v2 anymore.
Well truth be told I had a 4$ version of the thrunite C2. It charges 18650s to 4.19V at 0.89amp max and could only output the same, and I was using that when travelling as my only 18650 charger.
This cheapo version is no longer sold for 4$. I'd bought 4 and gave 3 away with some laptop extracted batteries whose capacity was questionable, But with a Panasonic NCR18650B, they can take my Samsung S4 mini from 8% to about 85% while still using the phone to play music over bluetooth while pinging towers and being a phone.