Other codes for PP3 batteries: 6F22, 6LR61, MN1604, 0068, A1604. GP Lithium 9V is the best choice of battery for smoke detectors. It provides a 10-year service life, highest energy density, stable discharge voltage & wide operating temperature which outperforms any comparable 9V battery. It also lasts up to 5 times longer than ordinary alkaline 9V batteries making it the best consumer replacement battery for 9-volt devices in home safety, wireless microphones, meters, & recreation applications etc. 100 percent free of Mercury, Lead, Cadmium. The U9VL-J battery has the highest energy density, most stable discharge voltage curve, longest shelf life, greatest operating temperature range & is lighter in weight than any comparable 9-volt battery.