DIAGNOSIS A solid red light usually means the charger is trying to charge but can't complete the process. This often points to a battery that's deeply discharged or has a faulty cell, but the charger itself can also be the problem.
FIX First, unplug the charger from the wall for 30 seconds. Replug it without the battery. The light should be green (ready). If it's still red with no battery, the charger is faulty. If it goes green, insert the battery. If it stays red for more than 8 hours, try a 'wake-up': put the battery on the mower and run it until it completely dies, then try charging again. Sometimes this resets the battery's management system.
IF THAT DIDN'T WORK Try charging a different 60V Toro battery with your charger, and try your battery on a different charger if possible. This will tell you which component is failing. The chargers have been known to fail.
HEADS UP Don't leave a battery on a stuck red-light charger for days. It can overheat. Lithium-ion batteries shouldn't be stored fully discharged—if you won't use the mower for a month, give the battery a partial charge (like 50%).