Hello I will help you with your question,
If you have automatic controls (set the temperature and the controls do the rest) you have a blower speed controller that may have failed. If you have the individual fan switch there is a bolwer resistor that may have failed.
In either case there is a blower relay, fuse and the blower motor itself that may be the problem. No battery to replace.
If you have a test light and will tell me which type of system you have I can help you test to find the faulty component
Let me know what I can do to help you with this