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Mazda MX-5 Miata 12V Automotive Battery Replacement Guide
How to change a weak or dead 12 volt car battery in a 4th generation ND 2016 to 2021 Mazda MX-5 Miata.

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2018 Miata Engine Bay
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12V Battery - Right Side
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Loosen Negative Terminal

This automotive maintenance tutorial was specifically written to assist owners of the 4th generation ND (2016, 2017, 2018, 2019, 2020 & 2021) Mazda MX-5 Miata in diagnosing and changing a weak or dead 12V automotive battery for the SkyActiv-G 2.0 PE-VPS 2.0L I4 engine.

Owners of other Mazda vehicles such as the Mazda2 (Demio), Mazda3 (Axela), Mazda5, Mazda6 (Atenza), CX-3, CX-5, CX-7, CX-9, RX-8 and MPV may also find these DIY instructions to be helpful.

A few symptoms of a weak or failing 12 volt car battery are slow starting / cranking, headlights that dim at a stop light or needing to be jump started on a cold morning. You can use a digital multimeter to see if the alternator is working properly by outputting about 13.7V to as much as 14.2 volts when the engine is running. If the alternator is working properly, see if the battery's voltage is at least 12.4 volts after a long drive when it has had time to charge and the engine is turned off. If not, it should be replaced.

The OEM 12V battery group size for an ND generation Miata is "51R".

A few compatible replacement aftermarket batteries are the Optima Batteries 8073-167 D51R, Exide Edge FP-AGM51R and the EverStart MAXX-51R (at Walmart).

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



 

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Pull Off Negative Terminal
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Cover & Tuck Away
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Loosen Two Nuts
The first two steps are to open the hood and then move to the right (driver) side of the engine bay.

The 12V automotive battery is located to the right of the engine air filter box and to the left of the fuse box.

First, loosen the "-" negative terminal nut (on the front of the battery located closer to the driver side headlight assembly) by turning it in the counterclockwise direction with a 10mm socket and a 1/4" drive ratchet.

Carefully pull the negative terminal off the battery post, wrap it in a small towel and tuck it away on the right side of the battery to help prevent electrical contact.

The battery is held in place by a black metal clamp and two "J" hook bars.

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Loosen Second Nut
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Battery Hold Down Bar
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Open Plastic Cover
Loosen the two nuts on the top of the battery hold down clamp attached to the "J" hook bars by turning them in the counterclockwise direction with a 10mm wrench or a 10mm socket with a 1/4" drive ratchet.

You don't need to fully remove the two nuts. Just loosen them enough so that you can slip the two "J" hook bars off their mounting brackets attached to the side of the plastic battery tray.

Carefully lift the battery hold down bar and the two "J" hooks off the old battery. Try to avoid making contact with the battery posts or the terminals.

Set the clamp aside in a safe place.

Squeeze the front of the black plastic cover on the positive terminal before flipping it open.

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Positive Terminal Cover
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Loosen Counterclockwise
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Pull Off Positive Terminal
Loosen the nut on the positive terminal a few turns in the counterclockwise direction with the 10mm socket and a 1/4" drive ratchet.

Pull the positive terminal off the "+" battery post.

Close the plastic cover over the positive terminal and tuck it away on the rear edge of the old battery to help prevent accidental electrical contact.

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Tuck Away "+" Terminal
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Pull Off Heat Shield
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Lift Out Old Battery
Pull the plastic and foam heat shield cover off the old battery and set it aside for re-installation later on.

Carefully lift the old battery out of the engine bay.

Gently set the old battery down on the ground. Avoid dropping the battery or tipping it over to prevent from having acid leak out.

Be sure to bring the old battery with you to Walmart or the auto parts store to prevent from having to pay a "core", "recycling", "disposal" or "environmental" fee.

If you can wait a few days for delivery, I highly recommend buying the Optima 8073-167 D51R battery since it has excellent reviews on Amazon.

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Old Battery Removed
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20HR 45Ah CCA 325A
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46B24L(S)-MF
The original OEM 12V battery was marked as part number Panasonic 46B24L(S)-MF (EL LFG1 A). The specs on the label are 20HR 45Ah CCA 325A B24 (JIS).



 

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Clean Off Battery True
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Lower In New Battery
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Replace Battery Box
Clean off any debris on the black plastic tray in the engine bay so that the new battery will rest evenly on it.

Carefully lower the new battery into the engine bay with the negative "-" post located at the front (closer to the headlight) and the positive "+" post located at the rear (closer to the windshield).

Slide the heat shield cover over the new battery.

If you've had an issue with corrosion (white or blue powder) building up on the terminals or the battery posts, consider installing some felt anti-corrosion washers over the battery posts.

The washers are cheap insurance against having corrosion damage your terminals or battery cables to the point where they need to be replaced.

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Push On Positive Terminal
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Tighten Terminal Nut
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Close "+" Plastic Cover
First, push the positive terminal (red plastic on the cable)  on to the "+" battery post.

Tighten the terminal nut a few turns in the clockwise direction with the 10mm socket and a 1/4" drive ratchet until is snug.

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

Flip the black plastic cover closed over the positive terminal.

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Lower Hold Down Clamp
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Two "J" Hook Bars
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Secure Hook To Mount
Carefully lower the hold down clamp and the two "J" hook bars down over the new battery.

Avoid making contact with the battery terminals or posts.

Re-attach the two "J" hooks to their mounting brackets on the side of the tray.

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Left Side J Hook Secured
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Tighten Two Nuts
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Tighten Nut Clockwise
Tighten the two nuts on the hold down bar in the clockwise direction with the 10mm socket or wrench until they are snug.

Check to see if the new battery can be moved, slid or rocked around on the tray.

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

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Push On Negative Terminal
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Tighten Nut Clockwise
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New Battery Installed
Push the negative terminal over the "-" battery post.

Tighten the 10mm nut in the clockwise direction until it is snug.

Double check that the two terminals are secure and that the new battery can't be moved.

To test the new battery, start the engine and turn on the headlights.

Be sure to record the battery change in your vehicle's service records.

For more, check out all of my 2016-2021 Mazda MX-5 Miata DIY Repair & Maintenance Guides.
 

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