I noticed that my battery tender has not shown a green light in quite a while. When I entered the garage where I am storing the car, there was a very strong sulphur smell, like you would get from a catalytic converter. Does this suggest a battery problem. I don't have a battery tester although there seems to be a strong enough charge to power lights, etc. I put it on a regular charger for the day. Any thoughts regarding a potential battery problem Thanks.