The numbers refer to the battery's diameter & length in mm. A 14500 batt has a diameter of 14mm, a length of 50mm & the last "0" indicates its round. The 5V PV you talk about either has a booster chip which bumps the 3.7 V up to 5 or it has a regulator which bumps the 7.4V down to 5. Im not sure how that mod works.