Popular wisdom is that the Scud batteries from Lucia Lui are about the best available, they're quoted as 1445mAh and this is realistic, they've been measured at 1400-1500mAh by multiple users. Mine measured in at ~1430mAh when I got it (according to bq27200) and reports at ~1350mAh now, on the same device, after nine months of use. Hopefully your BL-5J comes good after a few charge cycles, but if not - try a Scud.