Honda Fit 12V battery size and replacement
The short answer
A 2008 Honda Fit sold in the United States and Canada generally takes a Group 51R 12-volt battery. This applies to the first-generation Fit with the 1.5-liter gasoline engine, which was offered with either a manual or automatic transmission. Transmission and trim (base or Sport) are not known to change the battery group for that model year in North America.
Two conditions can change the answer. First, if the car was built for a different market, the battery may differ (see below). Second, a previous owner may have installed a non-original battery or modified the tray. Before buying, check the label on the battery currently in the car and the battery specification in the owner's manual.
What "Group 51R" means
A battery group size is an industry code that sets the case dimensions and the terminal layout, so the battery fits the tray, the hold-down clamp and the existing cables. The "R" means reversed terminals: the positive and negative posts are swapped compared with a standard Group 51.
This matters in practice. A plain Group 51 battery is the same physical size, but its posts sit on the opposite sides. In the Fit, the original cables may not reach, or may be stretched or misrouted. Unless you are sure the layout matches, choose a 51R rather than a 51.
Market differences to be aware of
The 2008 model year does not mean the same car everywhere. In North America, the 2008 Fit was still the first generation. In Japan and some other markets, the second-generation Fit (sold as the Jazz in some regions) was already on sale. Those vehicles may use batteries labeled with a different sizing system, such as Japanese JIS codes, rather than a BCI group number like 51R.
This article does not have verified battery specifications for non-North American 2008 Fit or Jazz models. If your car is an import or was sold outside the United States and Canada, go by the original battery's label, the owner's manual, or a Honda parts counter using your VIN.
Choosing a replacement
Group size: match 51R so the battery fits the tray, the hold-down and the cables. Cold cranking amps (CCA): this rating shows how well the battery starts the engine in cold weather. Choose a battery that meets or exceeds the CCA printed on the original battery or listed in the owner's manual. Going higher is generally fine; going lower can make cold starts harder. Reserve capacity: this shows how long the battery can run electrical loads if the alternator stops charging. Higher is generally better if you can compare it at similar prices. Battery type: a conventional flooded lead-acid battery matches what the car was designed for. An AGM (absorbent glass mat) version in the same group size is optional and typically costs more. The original 2008 Fit does not require AGM. Manufacture date: batteries lose charge on the shelf. Check the date code and avoid units that have been in stock for a long time.
Specific CCA figures, prices and warranty terms vary by brand and retailer, and none are given here. Compare these on the product label or listing.
Replacement notes
Replacing the battery on this car is usually a basic job with common hand tools. The general sequence is:
Turn the ignition and all accessories off. Disconnect the negative (black) cable first, then the positive (red) cable. Remove the hold-down clamp and lift out the old battery. Batteries are heavy and contain acid, so keep the battery upright. Clean any corrosion from the cable ends and tray. Set the new battery in the same orientation, secure the hold-down, then connect the positive cable first and the negative cable last. Tighten the terminals so they cannot be twisted by hand, without overtightening.
After the battery has been disconnected, some Honda audio units need an anti-theft code before they will work again. Whether your 2008 Fit's radio requires one depends on the installed unit. Check the owner's manual or the code card supplied with the car before you disconnect anything. Clock and radio presets may also need resetting.
Old lead-acid batteries should not go in household trash. Most battery retailers accept them for recycling, and some apply a core charge that is refunded when the old battery is returned.
Before you buy
For a North American 2008 Honda Fit, start with a Group 51R battery that meets or exceeds the original CCA rating. Confirm this against the label on the battery in the car, especially if the car's history or market of origin is uncertain. If the label and the 51R recommendation disagree, check with a parts counter using the VIN before buying.