ive had my provari for about a year and a half. im having a problem with battery drainage. i can put a freshly charged battery in reading 4.1 and after about 20 hits on it , the battery reads 3.7. i have cleaned it inside and out with alcohol. im kind of frustrated with it. i hate to pay that much and not use it. could my batteries be bad? can i use other 18650 batteries besides the aw batteries?