The KN-COPP-3 carbon monoxide (CO) detector is an AC powered device and the 9-volt battery is intended to supply a short-term backup during a power outage. According to the detector owner's manual, in the event of a power outage, the (alkaline) battery will continue operating the alarm for at least 20 hours. RAYOVAC®'s 9V lithium battery will last for up to five times longer, or about 100 hours in the event of a power outage. It will not last for 10 years in this device. Our 10 year life warranty is for battery use in ionization smoke alarms, and does not apply to CO detectors.
According to the KN-COPP-3 owner's manual it is recommended that the (alkaline) battery is replaced at least every six months. When using our lithium battery, that replacement time can be extended by up to 5 times, or approximately every 2.5 years. At 5 years, your battery lasted about twice as long as expected.
Additionally, the detector is designed to last for 7 years of operation under AC power, at which time it will provide an alert indicating that it should be replaced.