First off, if you did the recent update right now, SBF'ing won't work period it seems. AT least until a new SBF is leaked that works as Gasai Yuno stated.
Anyways, as I stated in my previous post, you're going to need to charge that battery manually. It will NOT charge VIA USB from my experience. Something to do with the system not working, or the usb power supply not being enough to charge the battery in bootloader mode, or something. Either way in my experience, USB CHARGING... WILL... NOT... WORK!!! (If and When you SBF successfully, then it will work again.))
You can look for a motorola direct battery charger online, but they aren't super cheap. At least they are meant for your battery. I did mine with that tool I listed, the Lenmar battery charger clip, and it worked for me. It was like, 5-9 bucks at Staples in the United States, and can be ordered online. But be careful with it, and make sure both tips are touching, which are the outside spots on the battery. The clip will turn green if you got it right. Let it charge for about a half-hour or so.
Or, you can get a new battery, and hope it was pre-charged already. At Verizon stores, most are charged to at least 50%, which is enough for you to SBF. I know from experience since that was what I did first. (I got the battery free though.)
Or you can look online and cut up your charging cable and tap the ends to the battery. I don't recommend this, since even though it's basically the same method as the clip charger, you still gotta deal with human error and such. At least the clips will light up if you got the contacts in right before you plug it in. I don't recommend this, but hey, it's your battery.
Or you can send your phone in.
However, all of this is useless right now if you did the apparent update, from what Gasai Yuno has stated.