MagTek BulleT MagneSafe - Manual (Page 15)

Section 3. Operation
9
CHARGING THE BULLET READER BATTERY
As mentioned above (LED Indicator), the BulleT reader may indicate low battery at power up.
The first time this happens there will probably be sufficient battery available for several more
card swipes, but the battery should be charged soon. If the low battery warning is ignored and
the battery gets too low, the reader will refuse to power up until it has been charged.
Charge the reader by connecting it to any USB port on a running system or a compatible 5VDC
source. For best results, allow the battery to charge fully (until the LED goes to steady amber)
before using the reader again.