80 watt may not be enough to keep your battery charged against vampire draws like the detector. An 80 watt panel getting 6 hours of sun should make 30 amps or so of power a day. The vampire draw is probably in the 24 amp/day range or less. Not always good sun though. I wouldn't want to rely on that in case of a couple cloudy days.
Depending on how the system is wired you may be able to use the battery disconnect switch and have the solar still charging. If they have the SCC wired directly to the battery and not through the switch you can charge without the draw of the CO detector.