The TB-BOX from CQ-HAM provides extended DC power and antenna tuning in one very cool little box. Six 18650 Li-ion cells provide an additional 6800mAh. The wide range antenna tuner will match non resonant whips or other field expedient antennas. It includes a beautiful leather case. Designed by amateur radio operator bh5hde and available on eBay by searching for “TB-Box for Ft-818”. The fit, finish, and materials used are top notch! Mine even arrived with Panasonic NCR18650B batteries which are considered among the best.