Group 27 batteries are larger lead-acid batteries commonly used in RVs, boats, and some trucks

A Group 27 battery is a standard lead-acid battery size defined by the Battery Council International. The "27" refers to a specific set of physical dimensions and terminal placement, not the power output. Group 27 batteries are roughly 10.25 inches long, 6.8 inches wide, and 8.8 inches tall, making them noticeably larger than Group 24 batteries but smaller than Group 31 batteries.

These batteries are popular in recreational vehicles, travel trailers, fishing boats, and some pickup trucks because they hold more charge than smaller groups while still fitting in many standard battery compartments. They typically have two terminals on top of the case, and you'll find them in both starting (engine-cranking) and deep-cycle (sustained power) versions, depending on what your vehicle or equipment needs.

Key Takeaways

  • Group 27 batteries come in starting and deep-cycle types, and you must match the type to your vehicle's actual use — starting batteries for engines, deep-cycle for sustained power draw.
  • Cold cranking amps (CCA) and amp-hour (Ah) ratings tell you how much power the battery delivers; higher numbers mean more power, but you need the right amount for your equipment.
  • Group 27 batteries cost between $100 and $250 depending on quality and type, and prices vary by retailer and whether you're buying a single battery or a pair.
  • Proper installation requires matching the battery terminals to your vehicle's cables and securing the battery in its compartment to prevent movement.
  • Regular maintenance — checking water levels in flooded batteries, keeping terminals clean, and charging before long storage — extends battery life to three to five years.

Starting batteries versus deep-cycle batteries

The two main types of Group 27 batteries serve different purposes, and using the wrong type will shorten its life or leave you stranded. A starting battery is designed to deliver a large burst of power for a short time — exactly what an engine needs to crank and start. Starting batteries have thinner lead plates and lower internal resistance, which lets them push high current quickly. If you use a starting battery for sustained power draw (like running lights or appliances for hours), the plates will break down fast.

A deep-cycle battery is built to discharge slowly over hours or days and then be recharged many times. It has thicker lead plates and can handle repeated partial discharge without damage. Deep-cycle batteries are standard in RVs, boats, and off-grid solar systems. They deliver less peak power than starting batteries, so they won't crank an engine as well, but they'll power your fridge and lights all night without failing.

Some batteries are labeled "dual-purpose" and attempt to do both jobs, but they compromise on both — they're neither as good at starting as a true starting battery nor as durable for deep cycling as a true deep-cycle battery. For most vehicles and equipment, you're better off choosing the type that matches your primary use.

Understanding cold cranking amps and amp-hour ratings

Cold cranking amps (CCA) measure how much current a battery can deliver for 30 seconds at 0°F while staying above 7.2 volts. This number tells you whether the battery has enough power to start your engine in winter. A typical Group 27 starting battery ranges from 600 to 1,000 CCA. Your vehicle's owner manual or the battery compartment label will tell you the minimum CCA you need; buying a battery with lower CCA than recommended risks not starting in cold weather.

Amp-hours (Ah) measure total energy storage — how much current the battery can deliver over time. A Group 27 battery typically holds between 85 and 110 amp-hours, depending on the type and brand. For starting batteries, this number is less critical because you only use a small fraction of the capacity to start the engine. For deep-cycle batteries, amp-hours matter much more because you're drawing power steadily, and you need enough capacity to run your equipment until the next charge.

If you're powering an RV or boat, calculate your daily power draw (lights, fridge, water pump, etc.) and choose a battery with enough amp-hours to cover that load plus a safety margin. Many RV owners use two or more Group 27 deep-cycle batteries wired together to increase total capacity.

Cost and where to buy Group 27 batteries

Group 27 battery prices vary widely based on type, brand, and where you shop. A basic starting battery typically costs $100 to $150, while a quality deep-cycle battery runs $150 to $250. Premium brands and batteries with longer warranties cost more. Buying a pair of batteries (common for RVs) will cost roughly double a single battery, though some retailers offer discounts for multiple purchases.

You can buy Group 27 batteries at auto parts stores (AutoZone, O'Reilly, NAPA), big-box retailers (Walmart, Costco), online marketplaces, RV supply shops, and marine retailers. Prices and availability differ by location and retailer, so it's worth checking a few sources. Some retailers offer core charges — a refund when you return your old battery — which reduces your net cost.

Installation is usually free or low-cost at the retailer where you buy the battery. If you install it yourself, you'll need basic tools (wrench, wire brush) and about 15 minutes. Many retailers also handle battery recycling if you're replacing an old one.

How to install a Group 27 battery

Before you begin, make sure the engine is off and the keys are out of the ignition. Locate the battery compartment in your vehicle — it's usually under the hood, but some RVs and boats have batteries in a separate compartment. Check that the new battery's terminal configuration (top-post or side-post) matches your vehicle's cable connectors.

Disconnect the negative (black) cable from the old battery first, then the positive (red) cable. This order prevents sparks. Remove any hold-down bracket or strap securing the old battery, then lift it out carefully — batteries are heavy, so use both hands or get help. Set the old battery aside for recycling.

Place the new battery in the compartment and find it with the hold-down bracket. Connect the positive cable to the positive terminal first, then the negative cable to the negative terminal. Tighten both connections firmly — a loose connection causes starting problems and can damage the battery. If the terminals are corroded, clean them with a wire brush before connecting. Close any compartment covers and start the engine to confirm everything works.

Maintenance to extend battery life

Most modern Group 27 batteries are sealed and maintenance-free, but some older or specialty models have removable caps on top. If your battery has caps, check the water level inside every few months — the liquid should cover the lead plates. If it's low, add distilled water only (never tap water, which contains minerals that damage the battery). Do not overfill.

Keep the battery terminals clean and dry. Corrosion (white, blue, or green crusty buildup) reduces the connection and can prevent starting. If you see corrosion, disconnect the cables and scrub the terminals and cable ends with a wire brush and a mixture of baking soda and water. Rinse with clean water and dry thoroughly before reconnecting.

If you're storing your vehicle or equipment for more than a month, charge the battery fully before storage and check it monthly. A battery left uncharged will slowly discharge and may not recover. In winter, a battery loses power faster, so consider using a trickle charger (a low-power charger that keeps the battery topped up) during long storage. With proper care, a Group 27 battery typically lasts three to five years.

Troubleshooting common Group 27 battery problems

If your battery won't hold a charge, the battery itself may be failing — most batteries have a warranty of three to five years, and you can contact the manufacturer or retailer about a replacement. If the battery drains quickly even when the vehicle is off, you may have a parasitic drain (an electrical component drawing power when it shouldn't). A mechanic can test for this with a multimeter.

If the battery is only a year or two old and drains in cold weather but works fine in warm weather, low CCA is the likely cause — you may need a higher-CCA battery for your climate. If the battery works but the engine cranks slowly, the battery terminals may be corroded or loose; clean and tighten them before assuming the battery is bad.

Swelling or bulging on the battery case means internal damage, usually from overcharging or a manufacturing defect. Do not attempt to use a swollen battery — it may leak or fail suddenly. Contact the retailer or manufacturer about a replacement.

Frequently Asked Questions

Can I use a Group 27 battery in a vehicle designed for a Group 24?

It depends on the compartment size. Group 27 batteries are larger, so they may not fit in a space designed for Group 24. Measure your battery compartment before buying. If the Group 27 is too large, it won't fit safely and could damage the vehicle's wiring or compartment. Stick with the group size your vehicle was designed for.

What's the difference between a wet-cell and an AGM Group 27 battery?

Wet-cell (flooded) batteries have liquid electrolyte and require occasional water top-ups. AGM (absorbed glass mat) batteries are sealed and maintenance-free. AGM batteries cost more but last longer and handle vibration better, making them popular in RVs and boats. Both types come in Group 27 size.

How do I know if my Group 27 battery is fully charged?

A fully charged battery reads about 12.6 volts or higher on a multimeter when the engine is off. If it reads below 12 volts, the battery needs charging. Many chargers have a "fully charged" indicator light. If you're unsure, a mechanic or auto parts store can test it for you.

Can I connect two Group 27 batteries together for more power?

Yes. Connecting two batteries in parallel (positive to positive, negative to negative) doubles your amp-hour capacity while keeping voltage the same — useful for RVs and boats. Connecting them in series (positive of one to negative of the other) doubles voltage but not capacity — rarely needed for Group 27 batteries. Use heavy-gauge cable rated for the current and include a fuse near each battery.

What should I do with my old Group 27 battery?

Lead-acid batteries are recyclable and contain materials that are valuable and hazardous. Most auto parts stores and retailers accept old batteries for recycling, often offering a core charge (refund) when you buy a replacement. Never throw a battery in the trash — it's illegal in most places and harms the environment.