Someone correct me if I'm wrong but I thought it was recommended to never charge from a device in order to increase the life of the device. I haven't ever charged from a device with a removable battery.
I believe this is not exactly the best information. Then it depends on the device and how "king kong" you are in handling it.
IMHO: Most all dual battery mods do a (if it is an option) poor job of "balance charging". Almost always one battery will have more charge than the other. (Cubiod, SXminiQ, Sigelei213 as examples)
Single battery mods do much better as there is only ONE cell to charge. The possible draw backs here are:
- Charging on the mod is slower than a dedicated charger
- The mod may not charge all the way up to 4.2V
- "King kong" might break the mUSB connector
Personally, I don't care about #1 as I plug stuff in for charging over night (when measured my iStick Pico draws 0.95A on the USB cable, more than my dedicated charger!). #2 involves run time, I've never noticed much difference but then again I've moved onto 26650 mods (charge via USB on those as well). As far as #3, I take care of my stuff. I've never have broken a USB port.
I think most of us have countless electronic devices that charge via USB and think nothing of charging them. I sure don't.