12V Motorcycle Battery Size Chart | Measure Once, Buy Right

A 12-volt bike battery must match case length, width, height, and terminal layout, or it may not fit the tray or cables.

A 12V Motorcycle Battery Size Chart helps you do one job well: match the battery case to your bike before you spend money. That sounds simple. In real life, plenty of 12-volt batteries look close enough on a store page, then show up a few millimeters too tall, too wide, or with the posts on the wrong side.

That is why battery shopping should start with fit, not brand names or amp claims. If the case does not sit flat in the tray, if the hold-down cannot close, or if the leads need to stretch, the battery is wrong even when the voltage is right. Get the fit right first. Then compare capacity, cranking power, and battery type.

Why Size Matters More Than A “12V” Label

“12V” only tells you the system voltage. It does not tell you the shape of the case, the height under the seat, the post style, or the cable reach. Two batteries can both be 12 volts and still be a bad swap.

On a motorcycle, space is tight. The tray is small. The side panels, seat pan, airbox, and wiring loom leave little room for error. A battery that is only a bit taller can press into the seat base. One that is a bit longer can hit the tray wall. One with reversed terminals can force the cables across the top, which is never a smart fit.

That is also why old-school part codes still matter. They tell you more than voltage. They hint at the case family your bike was built around. Once you know that family, buying gets easier.

How To Read A Motorcycle Battery Code

A battery code is not just a catalog name. It points to a case family with set dimensions and a known terminal pattern. Brands then add their own prefixes, suffixes, and chemistry labels on top of that base.

The Pieces That Matter On The Bike

• Length, width, and height: These decide whether the case will sit in the tray and clear the seat or cover.
• Terminal side and layout: These decide whether the positive and negative leads reach without crossing.
• Case family: Codes such as YTX12-BS or 12N9-3A point you toward a known size group.
• Battery type: AGM, sealed, or flooded changes maintenance needs and vent setup.

Say your old battery reads YTX12-BS. The smart move is to match that code first, then check the printed dimensions on the battery page or datasheet. If you only shop by “12V motorcycle battery,” you are guessing.

How To Measure Your Old Battery Before You Buy

If your label is faded, you can still get the right fit with a ruler or caliper. Measure the battery you are taking out, not the empty tray alone. The tray can have gaps, spacers, or rubber pads that make the space look bigger than the battery it was built for.

1. Measure the length from side to side at the battery case, not across the terminals.
2. Measure the width across the narrow side of the case.
3. Measure the height from the bottom of the case to the top of the battery body.
4. Check terminal position with the battery facing the same way it sits in the bike.
5. Look for a vent tube on flooded batteries and any tray lip or strap that locks the case in place.

Write those numbers down in millimeters. That is the format most battery data sheets use. A few minutes here can save you from buying a case that is close, yet wrong.

12V Motorcycle Battery Size Chart By Common Case Code

The chart below covers common sealed AGM 12-volt motorcycle battery sizes found on many street bikes, scooters, dual sports, and ATVs. The BCI group size system is the backbone for this kind of fit check. Sizes can vary by a tiny margin between makers, so verify the exact battery page before you order.

Battery Code	Case Size (L × W × H mm)	Fit Notes
YTX4L-BS	114 × 71 × 86	Small AGM case used on light bikes and scooters.
YTX5L-BS	115 × 72 × 107	Same narrow footprint as YTX7L-BS, yet shorter.
YTX7L-BS	115 × 72 × 132	Same base size as YTX5L-BS with more height.
YTX9-BS	152 × 87 × 107	Low, wide case often used where height is tight.
YTX12-BS	150 × 87 × 130	Common mid-size AGM case for many street bikes.
YTX14-BS	150 × 87 × 145	Same footprint family as YTX12-BS, yet taller.
YTX20-BS	175 × 87 × 155	Larger case with strong starting output.
YTX20HL-BS	175 × 87 × 175	Tall high-output case; check seat and strap room.

Notice the pattern. Some batteries share the same footprint and only change in height. That means a “close” swap can still fail. A YTX14-BS may fit the tray width and length of a YTX12-BS slot, yet the added height can stop the cover from closing. The reverse swap can fit the tray, yet leave you with less starting power than the bike was built around.

Terminal Layout And Tray Clearance

Case size gets all the attention. Terminal layout trips up a lot of buyers too. A battery can match every exterior number and still be a pain if the posts face the wrong way. Cable length on motorcycles is rarely generous.

• Check which side the positive post sits on when the battery faces you in the installed position.
• Check whether the screws drop in from the top, side, or front.
• Check hold-down bars, rubber blocks, and seat-pan clearance.
• Check whether your bike uses a vented flooded battery or a sealed AGM design.

Yuasa’s motorcycle battery choice notes say the replacement battery should meet or exceed the original voltage, technology, and specs. That is the cleanest way to think about it: match fit first, then match the electrical side.

Where Buyers Get Tripped Up

The most common miss is chasing a higher amp number without checking height. The next miss is swapping from a flooded code to a sealed code with a different terminal setup. Then there is the “it looks close enough” buy. That one creates most return labels.

Common Conventional 12V Case Sizes

Older bikes, vintage machines, and some service manuals still point to flooded 12N and B-series codes. These cases do not line up one-for-one with sealed YTX codes, so use the chart below when you are working from an older part number.

Battery Code	Case Size (L × W × H mm)	Fit Notes
12N5-3B	121 × 60 × 130	Small flooded case used on older light bikes.
12N5-4B	121 × 60 × 130	Same case family with a different terminal pattern.
12N7-3B	135 × 76 × 132	Common vintage size with narrow width.
12N7-4B	135 × 76 × 132	Same dimensions; terminal setup differs.
12N9-3A	135 × 76 × 139	Slightly taller case than 12N7 sizes.
B12A-A	134 × 80 × 159	Mid-height conventional case used on older street bikes.
B14L-A1	133 × 90 × 167	Wider case; left-side layout check matters.
B16-B	175 × 99 × 156	Larger conventional case for bigger engines.

This is where many mixed-up listings start. A flooded battery and a sealed AGM battery can sit in the same broad size range, yet the posts, venting, and height details can still differ. If your bike left the factory with a vent tube, do not ignore that piece when you shop.

Picking The Right Replacement Without Guesswork

Use this order every time:

1. Match the original code from the battery or owner’s manual.
2. Match the full case size in millimeters.
3. Match terminal side and terminal style.
4. Match battery type: flooded for flooded, AGM for AGM, unless your bike maker approves a change.
5. Then compare amp-hour and cranking numbers within the same fit class.

If you are between two choices, do not gamble on the one that “should fit.” Pull the seat, recheck the old case, and look at the battery page again. Motorcycle battery trays leave little room for luck.

A Smart Way To Use This Chart

Use this chart to narrow the case family, not to replace your bike manual. If the old battery label is readable, treat that code as your first anchor. If the label is gone, measure the old case and compare those numbers line by line.

Once length, width, height, and terminal layout all line up, you are in good shape. That is the whole point of a good battery size chart: less guessing, fewer returns, and a battery that drops into the tray the first time.