Owners of other Mazda vehicles such as the CX-5, CX-3, CX-30, MX-30, CX-8, Mazda8 (MPV), MX-5 Miata, Mazda2 (Demio), Mazda3 (Axela), Mazda6 (Atenza) and Mazda5 (Premacy) may also find these DIY instructions to be helpful.

The OEM (original equipment manufacturer) 12V battery is a "Group Size" 35 and the part number is Panasonic 55D23L-MF.

A few compatible replacement aftermarket batteries with their part numbers are as follows: Optima 8020-164 35 RedTop, Delphi BU9035 (AGM), Everstart MAXX-35N (Walmart), Interstate Batteries 35 8850242 (Costco) and Exide S35.

The tools needed to complete this procedure include a deep well 10mm socket with a 1/4" or a 3/8" drive ratchet or a standard 10mm wrench.

Please proceed with caution and at your own risk.

The first two steps are to open the hood and then move to the right (driver) side of the engine bay.

The 12 volt car battery is located behind the engine air filter housing and to the left of the electrical fuse box.

Locate the two nuts on the top of the black metal hold down bar or "clamp".

You don't have to fully remove the two nuts.

Just loosen them enough until you can detach the two "J" hooks at the bottom of the silver metal bars from their mounting slots.

Carefully lift the hold down clamp and the two "J" hooks off the top of the old battery.

Avoid making contact with the two battery terminals!

Set the hold down clamp and the two "J" hook bars aside in a safe place.

First, loosen the "-" negative battery terminal by loosening the nut in the counterclockwise direction with the 10mm socket and a ratchet or a 10mm wrench.

You do not need to fully remove the terminal nut. Just loosen it enough so that the terminal can be lifted off the battery post.

Carefully pull the negative terminal off the "-" battery post.

Cover the negative terminal in a small towel and tuck it away behind the old battery to help prevent accidental electrical contact.

Loosen the positive terminal nut by turning it in the counterclockwise direction with the 10mm socket and a ratchet.

Carefully lift the positive terminal off the "+" battery post.

You may need to use a plastic pry bar tool in order to loosen the terminal from the post.

Set the heat shield aside in a safe place for re-installation later on.

Do NOT touch both the "+" positive and "-" negative electrical contacts at the same time to avoid being electrocuted!

Clean off any debris from the black plastic tray in the engine bay so that the new battery will rest evenly on it.

Lower the heat shield box over the new battery.

(If you replaced the OEM battery with another "35" group size battery, the heat shield should fit perfectly.

If you've had a problem with corrosion (white, blue or green powder) building up on the terminals or posts, you should consider installing some felt anti-corrosion washers over the battery posts. They are very cheap insurance against having to replace corroded battery terminals or cables.

Tighten the terminal nut in the clockwise direction until it is snug.

Try to avoid over tightening the terminal nut to prevent from cracking the battery post which could lead to an acid leak.

Flip the plastic cover closed over the positive terminal. The cover should "click" securely into place.

Tighten the negative terminal nut in the clockwise direction with the 10mm socket and a ratchet until it is snug.

Avoid over tightening the terminal nut to prevent from damaging the battery post.

Double check that the battery terminals are securely attached to the posts.

Avoid making contact with the battery terminals or the posts.

Re-insert the left and right side "J" hooks into their mounting slots on the battery tray.

Make sure the new battery is securely in place. Try to move, slide and rock the new battery.

If the new battery can be moved around, tighten the two nuts on the hold down bar an extra turn or two.

Please remember to adjust the time on the clock and re-program your favorite radio stations before you start driving.

To test the new battery, start the engine.

If you suspect that your alternator is weak or might be failing, use a digital multimeter tool to check the voltage when the engine is running.

If the alternator is working properly, the voltage on the battery terminals should be about 13V to just over 14V when the engine is running.

If the engine is switched off, the new battery should read at least 12 volts and about 12.6 volts when fully charged.

Be sure to write down the battery change in your SUV's service records.

For more, please check out all of the 2016-2021 Mazda CX-9 DIY Repair & Maintenance Guides.