From what I've read, the charging failures via USB are not the battery, but the charging circuit in the mod. Some devices are specified as ok for pass-thru, others maybe not, and if you vape them while charging may fail. (Which may be the reason for the few casualties that have happened.)
In any event, if it's a battery failure while charging in an external charger, your mod is still ok...
Being able to swap in a fresh battery and go, and charge when convenient is my preferred mode.