I just purchased the ST1502S unit which comes with a battery, charger and the 15 inch hinged trimmer. There is also a promotion going on at Home Depot that also included an extra battery. However, while I found the serial number for the trimmer and the charger, I cannot find a serial number on either the included battery or the extra battery. I looked at the picture the website included showing the serial number is supposed to be on the side sticker where the battery slides in. I have the warning stickers on both inside sides, but NO serial number. What is your suggestion?