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Group 27 Marine Battery Guide: Pro-Guide 27M800 (800 CCA, 182 RC)
Short answer: A Group 27 marine battery gives you more room for lead than a Group 24, and the Pro-Guide 27M800 uses that room for both jobs a boat battery has to do. This 12V flooded lead-acid battery delivers 800 cold cranking amps (CCA), 1,000 marine cranking amps (MCA) and 182 minutes of reserve capacity (RC) at 25 amps in a standard Group 27 case (12 1/16 x 6 13/16 x 8 7/8 in, 49 lb). That combination of strong starts and long accessory runtime makes it the most balanced battery in our flooded dual purpose line.
Many boats ship with a Group 27 tray because it is the sweet spot between compact Group 24 batteries and big, heavy Group 31s. In this guide we cover what a Group 27 marine battery is, how the 27M800's numbers translate to real starting and runtime, how flooded compares with AGM and lithium, and how to charge and maintain it for the longest possible service life.
Key Takeaways
- Strong starts: 800 CCA, 1,000 MCA and 1,000 CA.
- Long accessory runtime: 182 minutes of reserve capacity at 25 amps, about 35% more than the Group 24 24M800.
- Standard Group 27 case: 12 1/16 x 6 13/16 x 8 7/8 in, so it fits common Group 27 boxes and trays.
- Weight: 49 lb (22.2 kg).
- Warranty: 12 months free replacement and 30 months total pro-rata coverage.
What Is a Group 27 Marine Battery?
"Group 27" is a case-size standard from the Battery Council International (BCI). It describes the outside dimensions of the battery, not what is inside. A Group 27 is about the same width and height as a Group 24 but longer: the 27M800 is 12 1/16 in long versus 10 1/4 in for our Group 24 models, which leaves room for more plate material. In a lead-acid battery, more plate material generally means more cranking power, more reserve capacity or both.
Group 27 batteries are popular in bass boats, walleye rigs, pontoons and center consoles because they hit a practical middle ground. They are noticeably more capable than a Group 24 without the extra length and weight of a Group 31.
The Pro-Guide 27M800 is a flooded (wet cell) lead-acid battery. Its label reads Starting, and Pro-Guide lists it as a dual purpose battery: it is built first to crank your engine, with enough reserve capacity to run electronics, lights and pumps when the engine is off.
Pro-Guide 27M800 Specifications
| Model / SKU | Pro-Guide 27M800 (PGM27M800) |
| Type | Flooded lead-acid, starting / dual purpose |
| Voltage | 12V |
| BCI group size | 27 |
| Cold cranking amps (CCA) | 800 |
| Marine cranking amps (MCA) | 1,000 |
| Cranking amps (CA) | 1,000 |
| Reserve capacity (RC) | 182 minutes at 25 amps |
| Charge current | 10A standard, 15A maximum |
| Dimensions | 12 1/16 x 6 13/16 x 8 7/8 in (306.4 x 174.6 x 228.6 mm) |
| Weight | 49 lb (22.2 kg) |
| Warranty | 12 months free replacement, 30 months total pro-rata |
Download the 27M800 data sheet (PDF) for your records.
The 27M800 label shows its three headline numbers: 1,000 MCA, 800 CCA and 182 minutes of reserve capacity.
Starting Power and Reserve Capacity Explained
A dual purpose battery is judged on two things: how hard it can crank and how long it can carry accessories. The 27M800 is strong on both.
Cranking: 800 CCA and 1,000 MCA
Cold cranking amps (CCA) measure the current a battery can deliver for 30 seconds at 0°F while holding a usable voltage. Marine cranking amps (MCA) run the same test at 32°F, closer to typical boating conditions. Your outboard's owner's manual lists a minimum MCA or CCA. The 27M800's 800 CCA and 1,000 MCA cover a wide range of outboards and give you margin for cold mornings and an aging battery. Always confirm against your engine's requirement.
Reserve capacity: 182 minutes
Reserve capacity (RC) is how many minutes a fully charged battery can supply 25 amps before dropping to 10.5 volts. At 182 minutes, the 27M800 can deliver roughly 76 amp-hours at that rate. That is the number that matters if your engine's charging system fails, or if you sit on a spot for hours with graphs, lights and a livewell running.
Why the combination matters
Many batteries trade one for the other: big cranking numbers with modest reserve, or deep reserve with lower cranking. The 27M800 gives you the same 800 CCA as our Group 24 24M800 plus 47 more minutes of reserve capacity, which makes it a strong fit for single-battery boats that run a lot of electronics.
How Long Will a Group 27 Battery Run Your Accessories?
Because this battery has to start your engine at the end of the day, plan to use only about half of its capacity before recharging. Using the RC math above (roughly 76 amp-hours at a 25A draw), that leaves about 38 amp-hours for accessories. Rough estimates:
| Load | Typical draw | Rough runtime to about 50% |
| Single fish finder | About 1.5A | About 25 hours |
| Two graphs plus nav lights | About 4A | About 9 to 10 hours |
| Livewell aerator, graphs and lights | About 8A | About 4 to 5 hours |
| Stereo, lights and electronics on a pontoon | About 12A | About 3 hours |
These numbers are estimates. Lead-acid batteries usually deliver a little more total capacity at light loads than the RC test suggests, and less in cold weather or as they age. If your electronics run all day while you fish, a dedicated house or electronics battery keeps your cranking battery fresh. Read Should You Run a Separate Battery for Your Boat Electronics? for the pros and cons.
Group 27 Flooded vs. AGM vs. Lithium
Group 27 batteries come in flooded, AGM and lithium versions. Here is how they typically compare for a starting and accessory job:
| Factor | Flooded (Pro-Guide 27M800) | Typical AGM | Typical lithium (LiFePO4) |
| Up-front cost | Lowest | Higher | Highest |
| Maintenance | Periodic water and terminal checks | Sealed, no watering | Sealed, no watering |
| Usable capacity | About 50% of rated | About 50% of rated | Most of rated capacity |
| Mounting | Upright, ventilated location | Sealed, more flexible | Sealed, more flexible |
| Charging | Standard flooded profile | AGM profile | Lithium profile required |
| Weight | 49 lb | Usually similar or heavier | Usually much lighter |
If you can reach the battery for occasional checks and want the most starting power and reserve per dollar, flooded is typically the value choice. Prefer sealed and maintenance-free? Browse our AGM batteries. Want to cut weight and run electronics deeper? See our dual purpose lithium batteries.
What Is the 27M800 Best For?
- Single-battery boats with lots of electronics: start the engine and run graphs, lights and a livewell with 182 minutes of reserve behind you.
- Cranking battery in a bass or walleye boat: pair it with a deep cycle trolling motor bank. Our guide One Pack or Three? Choosing the Right Trolling Motor Battery Setup explains how to wire it.
- Pontoons and family boats: stereo, lights and USB chargers draw steadily while you are anchored; the extra reserve gives you margin to start the motor afterward.
- Cold-weather anglers: 800 CCA delivers dependable starts in early spring and late fall.
The 27M800 is not designed to power a trolling motor day after day. For that job, use a deep cycle battery such as the Pro-Guide 27M180 Group 27 flooded deep cycle or a lithium deep cycle bank.
A molded carry handle makes the 49 lb 27M800 easier to lift into a Group 27 tray.
How to Charge a Group 27 Flooded Battery
Pro-Guide rates the 27M800 for a 10-amp standard charge and a 15-amp maximum.
- Use a marine charger with a flooded lead-acid setting. A smart charger tapers current as the battery fills and holds it at float without overcharging.
- Match the charger to the battery. The Pro-Guide 12V 10A 1-Bank Battery Charger lines up with the 10A standard rate. In a boat with a 24V or 36V trolling bank, a multi-bank charger like the 12V 10A 3-Bank or 12V 10A 4-Bank charges every battery at once.
- Recharge promptly. Lead-acid batteries left partially discharged lose capacity to sulfation over time.
- Charge in a ventilated area. Flooded batteries typically release small amounts of hydrogen near full charge, so keep sparks and flames away.
As a rough estimate, replacing about 38 amp-hours with a 10A charger takes around four to five hours, allowing for charging losses and the slower top-off stage.
Installation and Maintenance Checklist
Confirm the fit
Measure your tray or box before ordering. The 27M800 is 12 1/16 in long, 6 13/16 in wide and 8 7/8 in tall, and you need clearance for the terminals and cable ends above that.
Mount it upright and secure
Flooded batteries must stay upright. The NOCO Group 27 Snap-Top Battery Box and NOCO Group 27 Battery Tray are sized for Group 27 batteries like the 27M800.
Check the water
Flooded batteries typically lose some water over a season. Check monthly that the plates are covered, top up with distilled water only (preferably after charging) and never overfill. Wear eye protection.
Protect the terminals
Clean and tighten the connections, then coat them with battery corrosion preventative spray to keep starts strong.
Store it charged
For winter, charge fully, disconnect and keep it on a maintainer or recharge every few weeks to prevent sulfation and freezing. Our marine battery maintenance guide has the full checklist.
27M800 vs. 24M800 and 31M225: Which Should You Choose?
| Spec | 24M800 | 27M800 | 31M225 |
| Group size | 24 | 27 | 31 |
| CCA / MCA | 800 / 1,000 | 800 / 1,000 | 675 / 845 |
| Reserve capacity | 135 minutes | 182 minutes | 210 minutes |
| Weight | 42 lb | 49 lb | 54 lb |
Choose the 24M800 if you only have a Group 24 space. Choose the 27M800 if you have a Group 27 tray and want top cranking power with long reserve. Choose the 31M225 if you have a Group 31 space and accessory runtime matters more than maximum cranking amps.
Frequently Asked Questions
What is a Group 27 marine battery?
It is a 12V battery in the BCI Group 27 case size, about 12 in long. The Pro-Guide 27M800 is a flooded Group 27 rated 800 CCA, 1,000 MCA and 182 minutes of reserve capacity.
Is a Group 27 battery better than a Group 24?
A Group 27 has a longer case, so it typically offers more reserve capacity. The 27M800 matches the 24M800's 800 CCA and adds 47 minutes of reserve capacity, but it needs a Group 27 space.
Can the 27M800 start my outboard?
Yes, if your engine's minimum requirement is within 800 CCA / 1,000 MCA. Check your outboard owner's manual.
How long will the 27M800 run a fish finder?
As a rough estimate, about 25 hours for a single fish finder drawing about 1.5A before reaching about 50% charge, based on its 182-minute reserve capacity.
Can I use the 27M800 for a trolling motor?
It is built mainly for starting and accessory loads, not repeated deep discharges. Use a dedicated deep cycle battery for regular trolling.
What charger do I need for a Group 27 flooded battery?
Use a marine charger with a flooded lead-acid setting. The 27M800 is rated for 10A standard and 15A maximum charge current.
How much does the 27M800 weigh?
The Pro-Guide 27M800 weighs 49 lb (22.2 kg).
Power Your Group 27 Tray with Pro-Guide
If your boat has a Group 27 tray and you want one battery that starts hard and keeps your electronics running, the Pro-Guide 27M800 delivers 800 CCA, 1,000 MCA and 182 minutes of reserve capacity in a standard Group 27 case. It is backed by a 12-month free replacement warranty and 30 months of total pro-rata coverage. The Pro-Guide 27M800 is sold through our dealer network, so call us at 1-800-827-3232 and we will point you to the closest dealer.
Questions about fit or cranking amps? Call our team at 1-800-827-3232 or browse all lead-acid batteries and marine accessories.
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