Put the battery on charge overnight. There is no LED indicator on the charger to tell if it is working or the battery is fully charged so a volt meter could be used to check voltage. It should read between 12 and 14.5 volts. My aftermarket batteries read 14.5 volts. The only way I can tell that the charger is working is it gets warm.
You have the Excalibur II so you have the NIMH batteries which is a plus. No need to worry about battery memory with the older style NICAD batteries.
Check the contacts for the battery to the control pod to make sure there is no corrosion on the contacts. When putting the connector on the battery pod, make sure you put some plumbers silicone grease around the connection. It will help keep out water,
I doubt that you did any damage by leaving it in your garage unless it was in direct sunlight for hours on end. Even then, the Excalibur is one tough metal detector and can stand quite a bit of abuse.
