Can I power the Fio v3 with a 4v lipo? Full charge is around 4.8v. Will the Fio charge such a battery if a USB cable is plugged in?
4.8 volts is a bit high for a Lipo. Are you sure you have a LiPo and not some other chemistry battery like NiMh? The built in charger on the Fio V3 will charge an attached battery up to 4.2 volts and then terminate the charge. Just make sure the polarity on your batteries plug matched the marking on the Fio V3’s jack. (All the SparkFun batteries do match.)
Yup, listed as a Getac 4v Lithium Polymer battery. Trying to find the datasheet again for it.