The Honda Fit uses a 12-volt automotive battery; the exact group size depends on the model year and market.
In practice, the 12-volt battery powers the car’s starter and electronics. If you have a standard gasoline Fit, you’ll need a 12-volt replacement in the correct group size for your year. If you own a Fit Hybrid, there is also a high-voltage traction battery, with the 12-volt battery serving ancillary systems.
Battery basics for the Honda Fit
How to confirm the right size for your car
Non-hybrid vs hybrid considerations
Common group sizes you might encounter
How to verify the size for your specific car
Summary
Bottom line: Honda Fits use a 12-volt automotive battery, with the exact group size varying by generation and market. Check the battery label or the owner's manual to confirm the correct group size, and choose a battery with matching CCA and RC for your climate. For Fit Hybrids, note there is also a separate high-voltage battery system.