A lithium-ion battery was blamed for setting off a carbon monoxide detector at a Madison home on Tuesday night. Firefighters responded to the house in the 100 block of Shiloh Drive, on the city’s west side, shortly after 9 p.m. when the alarm went off for what the homeowners said was the second night in a row. They found low levels of the deadly gas in the basement and determined the source was a lithium-ion battery charger that had two batteries on it. The firefighters began ventilating the basement while checking other appliances to make sure they were operating normally. No other potential CO sources were found. In its statement, MFD offered a reminder that lithium-ion batteries that are starting to show signs of damage should not be used. The fire department added the City of Madison offers resources to recycle them.