Battery Box Size Chart: Group 24, 27, 31 & U1 Box and Tray Sizes

Short answer: Buy the battery box or tray that matches your battery's BCI group size. A Group 24 battery is about 10 1/4 in long, a Group 27 about 12 in and a Group 31 about 13 in. All three are roughly 6 13/16 in wide. A Group U1 is much smaller, at up to about 7 2/3 x 5 1/5 in. The NOCO Group 24, Group 27 and Group U1 Snap-Top boxes each hold one battery of that size. The Group 24-31 box has an adjustable divider, so it fits anything from a Group 24 to a Group 31.

Battery boxes and trays are sold by group size, not by brand, so the size chart below is the fastest way to find the right one. We also cover how to measure your battery compartment, when to choose a box or a tray, plastic vs. metal, and the one fit problem lithium batteries can cause.

Key Takeaways

• Match the group size: boxes and trays are sized to BCI battery groups (U1, 24, 27, 31), so the group number on your battery tells you which one fits.
• Width rarely changes: Group 24, 27 and 31 batteries are all about 6 13/16 in wide. Length is what changes, from about 10 1/4 in to about 13 in.
• One box covers 24 to 31: the Group 24-31 box has an adjustable divider, so it can follow you through a battery upgrade.
• A box encloses, a tray secures: a box has a vented lid that covers the terminals. A tray holds the battery down with a strap and leaves the top open.
• Check height for lithium: most lithium batteries match their group's footprint, but tall Group 31 lithium batteries (10.83 in) need more headroom than most lead-acid batteries.

Battery Box Size Chart

The battery dimensions below come from the Pro-Guide batteries in each group. Lengths and widths vary by only a fraction of an inch between models, but height varies more, so check it against your lid and compartment.

Battery group	Battery length	Battery width	Battery height	Battery box	Battery tray
Group U1	6.85 to 7 2/3 in	4.84 to 5 1/5 in	6.42 to 6 4/5 in	NOCO Group U1 Snap-Top	—
Group 24	10 1/4 in	6 7/10 to 6 13/16 in	8 1/5 to 9 3/16 in	NOCO Group 24 Snap-Top or Group 24-31 box	NOCO Group 24 tray
Group 27	12 to 12 1/16 in	6 3/5 to 6 13/16 in	8 1/5 to 8 7/8 in	NOCO Group 27 Snap-Top or Group 24-31 box	NOCO Group 27 tray
Group 31	13 to 13 1/16 in	6 4/5 to 6.93 in	8 1/2 to 9 1/8 in	Group 24-31 box	NOCO Group 31 tray
Group 31 (tall lithium)	13.07 in	6.93 in	10.83 in	Measure inside height first	NOCO Group 31 tray

Need the dimensions and weight of a specific battery? Our battery group size chart lists every Pro-Guide model by group.

The Group 24-31 box's adjustable divider takes up the extra length when it holds a shorter Group 24 or 27 battery.

How to Measure for a Battery Box

The group number is the quickest way to choose, but measuring takes two minutes and avoids a return:

1. Find the group size on the battery label or in its listing (for example, "Group 31" or "BCI 24").
2. Measure the battery: length, width and height, including the terminals. Height to the top of the terminals is the measurement people most often miss.
3. Measure the space the box has to fit in: the compartment floor, plus the clearance under any hatch, seat or console. A box is larger on the outside than the battery it holds.
4. Allow room for cables: the box lid has to close over your terminal connections, fuses and ring terminals.
5. Plan the hold-down: decide where the strap or bolts will anchor before you drill anything.

Battery Box vs. Battery Tray

Factor	Battery box	Battery tray
What it is	A fully enclosed case with a vented lid	An open base the battery sits in, held down by a strap
Terminal protection	The lid covers the terminals	Terminals stay exposed, so use terminal boots
Access	Remove the lid to reach the terminals	Terminals are always reachable
Best for	Open decks, bilges, trailers, campers and any spot where tools or gear could touch the terminals	Dedicated battery compartments, consoles and anywhere headroom is tight
Pro-Guide options	NOCO Snap-Top U1, 24 and 27; Group 24-31 box	NOCO trays for Group 24, 27 and 31; HEAVYWEIGHT metal tray

The NOCO boxes and trays we carry state that they meet U.S. Coast Guard regulation 33 CFR 183.420 and ABYC standard E-10.7 for marine battery installations. Both styles hold the battery in place, which is the main job. Choose a box when the terminals need covering, and a tray when you need to reach them often or don't have the headroom for a lid.

Plastic vs. Metal Battery Boxes and Trays

Plastic (NOCO Snap-Top boxes and trays)

• Keep their impact strength down to -20°F and resist UV, oil, gas and other contaminants.
• Snap-Top boxes have locking tabs that hold the lid on, heavy-duty handles and full ventilation for battery gases.
• The U1 box and the trays have an internal reservoir that collects battery acid. The trays include a tie-down strap and also work with J-bolts and a tie-down clamp.
• Light and corrosion-proof, which suits most boats, RVs and trailers.

Metal (Pro-Guide HEAVYWEIGHT tray)

The HEAVYWEIGHT Metal Battery Tray weighs 38 lb on purpose. Anglers who switch to lithium sometimes lose weight in the back of the boat and change how it sits in the water. The HEAVYWEIGHT tray adds that weight back as a counterbalance while holding the battery securely.

Battery Boxes for Lithium Batteries

Most lithium batteries use the same group-size footprint as the lead-acid batteries they replace, so the same box or tray fits. The Pro-Guide 24M100, for example, measures 10 1/4 x 6 13/16 x 9 3/16 in and fits Group 24 boxes and trays. Three things are different:

• Height: Pro-Guide's high-capacity Group 31 lithium batteries, including the 12V 235Ah and the 16V, 24V, 36V and 48V tall models, use the Group 31 footprint but stand 10.83 in tall. That is roughly 2 in taller than our Group 31 lead-acid batteries (8 1/2 to 9 1/8 in). Measure the inside height of your box before you order. If the lid won't close, use a Group 31 tray and strap instead.
• Weight: a lithium battery can weigh half as much as the lead-acid battery it replaces. A lighter battery can still slide around, so it needs a strap or a box just as much.
• Venting: sealed LiFePO4 batteries don't vent gas the way flooded batteries do while charging, but a vented box does no harm. Keep it if it is the easiest way to secure the battery.

Installation Tips

• Anchor the box or tray, not just the battery. Screw or bolt it to a solid surface so the strap has something to pull against.
• Route cables before closing the lid. Pinched cables can wear through their insulation over time.
• Protect the terminals with boots when you use an open tray, and treat them with corrosion preventative spray.
• Add a shock absorber for boats that run in rough water. The Battery Shock Absorber cushions the battery against pounding.
• Check the strap every season. UV and heat wear straps out, and a loose strap is the first thing to go. See our marine battery maintenance tips.

Frequently Asked Questions

What size battery box do I need for a Group 31 battery?

Use a box made for Group 31 batteries, such as the Group 24-31 Plastic Battery Box. A Group 31 battery is about 13 in long and 6 13/16 in wide. For a tall Group 31 lithium battery (10.83 in), check the box's inside height first, or use a Group 31 tray.

Will a Group 27 battery fit in a Group 31 battery box?

It fits in the Group 24-31 box, which has an adjustable divider that takes up the extra length. A box sized only for Group 31 leaves room for the shorter battery to slide unless you fill the gap.

What are the dimensions of a Group 24 battery?

Pro-Guide Group 24 batteries are 10 1/4 in long, 6 7/10 to 6 13/16 in wide and 8 1/5 to 9 3/16 in tall, depending on the model.

What is the difference between a battery box and a battery tray?

A battery box encloses the battery and covers the terminals with a vented lid. A battery tray is an open base that holds the battery down with a strap and leaves the terminals exposed. Both keep the battery from shifting.

Can I put a lithium battery in a battery box?

Yes. Most lithium batteries share their group's footprint, so the same box fits. Check the height on high-capacity Group 31 lithium batteries, which are 10.83 in tall.

Do battery boxes need to be vented?

Flooded lead-acid batteries release gas while charging, so their boxes should be vented. All of the NOCO Snap-Top boxes we sell are fully ventilated.

Do I need a battery box on a boat?

The battery has to be secured so it can't shift, and its terminals protected from accidental contact. A box does both. A tray with a strap secures the battery, but the terminals need boots.

Find the Right Box for Your Battery

Choose your group size, then choose a box if you want the terminals covered or a tray if you want quick access. If you are upgrading to lithium, check the height before you order.

SHOP BATTERY BOXES

Looking for trays, hold-downs and mounting hardware? Browse mounting hardware and trays, or call our team at 1-800-827-3232 for help matching a box to your battery.

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