Group 27 Marine Batteries: Fit, Capacity and Options
Group 27 is the go-to size for many boaters. It’s the classic trolling motor battery, a common dual-purpose battery on pontoons and center consoles, and a popular house battery on small cruisers. This guide covers the size, what to expect from the ratings, and which group 27 batteries suit different jobs. Check product pages for exact dimensions and current specs.
Group 27 size
Typical BCI dimensions for a group 27 are about 12 inches long, 6.8 inches wide and 8.9 inches high, with terminals adding a little height. It’s about 1¾ inches longer than a group 24 and roughly an inch shorter than a group 31. Marine versions are often labeled 27M and may have dual terminals.
Types of group 27 batteries
| Type | Example in our store | Key ratings |
|---|---|---|
| Starting | Interstate 27M-XHD | 800 CCA, 1,000 MCA, RC 182 |
| Starting / heavy duty | Interstate M-27HDC | 675 CCA, RC 160 |
| Deep cycle (flooded) | Trojan 27TMX | 105Ah, RC 175, 55 lb |
| Deep cycle (flooded) | Trojan SCS200 | 115Ah, RC 200, 60 lb |
| Deep cycle (flooded) | Interstate SRM-27 | 88Ah, 600 CCA, RC 160 |
| Enhanced flooded | Interstate 27M-EFB | 90Ah, 675 CCA, RC 160 |
| Dual purpose AGM | Interstate 27M-AGM | 85Ah, 850 CCA, RC 182 |
| Dual purpose AGM | Interstate 27M-AGM-A | 90Ah, 750 CCA, RC 175 |
| Deep cycle AGM | Trojan 27-AES | 89Ah, RC 158, 66 lb |
| Lithium | Battle Born 100Ah 27/31 | 100Ah, 31 lb |
| Lithium | Interstate Li27M | 100Ah, RC 240 |
| Lithium 24V | EPOCH 24V 60Ah Pro | 60Ah at 24V, 30 lb, IP67 |
Group 27 for trolling motors
A group 27 deep-cycle battery is the traditional trolling battery: one for a 12V motor, two in series for 24V, three for 36V. In lead-acid, expect about 40–55Ah usable per battery if you stop around 50%. That’s enough for a half to full day of moderate trolling with a 12V motor.
Lithium makes a big difference here. A 100Ah lithium battery in a 27/31 case gives roughly 80–100Ah usable at 31 pounds, versus 55–66 pounds for lead-acid. For a 24V motor, EPOCH’s 24V 60Ah Pro replaces two group 27 batteries with one 30-pound case.
Group 27 for dual purpose
On boats with one battery, or one per engine, a group 27 AGM dual-purpose battery is a strong choice. Interstate’s 27M-AGM lists 850 CCA and 182 minutes of reserve, enough to start most outboards while running electronics and pumps. AGM is sealed and handles vibration well, which suits saltwater boats that pound through chop.
Group 27 for starting
For larger outboards, a group 27 starting battery like the 27M-XHD gives 800 CCA with a healthy reserve. Check your engine maker’s minimum cranking rating and use at least that.
Group 27 as a house battery
On small cruisers and center consoles, one or two group 27 deep-cycle batteries are often used as a house bank for lights, pumps, a stereo and small refrigeration. For heavier loads, consider group 31 lithium or a larger bank.
Weight
Lead-acid group 27 batteries in our listings weigh 55–66 pounds. A three-battery 36V trolling bank of lead-acid group 27s weighs 165 to almost 200 pounds. A lithium 100Ah in the same case weighs 31 pounds, so a three-battery lithium bank weighs about 93 pounds.
Flooded, AGM or lithium?
| Flooded | AGM | Lithium | |
|---|---|---|---|
| Upfront cost | Lowest | Middle | Highest |
| Maintenance | Watering | None | None |
| Usable capacity | ~50% | ~50% | Most of rating |
| Vibration resistance | Fair | Good | Good |
| Weight (group 27) | 55–60 lb | 66 lb (Trojan 27-AES) | ~31 lb |
| Cold charging | Fine | Fine | Needs heating or warm temperatures |
Charging
For lead-acid, a 10A–15A charger per battery recharges a group 27 overnight. Use the matching profile for flooded or AGM. Multi-bank onboard chargers keep each battery in a trolling bank charged separately, which helps keep the bank balanced. For lithium, use a LiFePO4 profile. Battle Born lists 14.2–14.6V for its 12V batteries.
Installation tips
- Use a group 27 box or tray with a strap. Lighter lithium batteries need to be secured just as firmly.
- Check that cables reach the terminals and that the terminal type matches your lugs.
- For series trolling banks, use identical batteries of the same age and type.
- Fuse the bank close to the battery.
How long does a group 27 last?
Service life depends on use and care more than size. Lead-acid deep-cycle batteries last longest when recharged promptly after every trip and kept out of deep discharge. Interstate’s group 27 lead-acid batteries list 12 to 36 months of free replacement, depending on the model. Lithium batteries list thousands of cycles and longer warranties; Interstate’s Li27M lists 60 months free replacement.
Signs it’s time to replace
- The battery won’t hold a charge overnight.
- Runtime on the water drops noticeably.
- A load test shows voltage falling below 9.6V at half the CCA rating for 15 seconds.
- The case is bulging or leaking.
Quick picks
- 12V trolling, light boat: Battle Born 100Ah 27/31 lithium.
- Pontoon with one battery: Interstate 27M-AGM.
- Budget 24V or 36V lead-acid trolling bank: two or three Trojan 27TMX batteries.
More reading
Compare sizes in group 24 vs 27 vs 31. See also group 24, group 31 and GC2 golf-cart batteries. For the full chart, read BCI battery group sizes explained. If you’re not sure which battery type you need, see cranking vs dual-purpose vs deep-cycle and the marine battery buying guide.
Products mentioned
Frequently asked questions
What size is a group 27 battery?
Typically about 12 x 6.8 x 8.9 inches. Check the product listing for exact dimensions.
How many amp-hours is a group 27?
Lead-acid group 27 batteries in our store list 85–115Ah. Lithium models list 100Ah.
Is group 27 good for a trolling motor?
Yes. It’s the most common trolling battery size.
How much does a group 27 battery weigh?
Lead-acid models weigh 55–66 pounds. A 100Ah lithium in a 27/31 case weighs about 31 pounds.
Can I use a group 27 to start my engine?
Yes, with a starting or dual-purpose model rated for your engine’s cranking needs.