Best Deep Cycle BCI Group 27 Batteries

BCI Group 27 batteries are very popular industrial, marine and automotive batteries, commonly designed as deep cycle or dual-purpose batteries, with cranking-only group 27 batteries being rather rare.

BCI Group 27 batteries are commonly used in applications where larger and more powerful BCI Group 31 batteries are too large and heavy, but strong and reliable battery is nonetheless, required, like UPS batteries, trolling motor batteries, in the security and medical systems, as wheelchair battery, as RV/ATV/SUV battery, etc.

northstar nsb agm27m

BCI Group 27 Batteries Features and Specifications

There are three sub-groups of the BIC Group 27 batteries, with their actual dimensions being given in the following comparison chart together with the dimensions of the BCI Groups 24 and 31:

BCI Group Size L (mm) W (mm) H (mm) L (inches) W (inches) H (inches)
Group 24 Batteries 260 173 225 10 1/4 6 13/16 8 7/8
27 306 173 225 12 1/16 6 13/16 8 7/8
27F 318 173 227 12 1/2 6 13/16 8 15/16
27H 298 173 235 11 3/4 6 13/16 9 1/4
Group 31 Batteries 330 173 240 13 6 13/16 9 7/16

As one can see, BCI Group 24 batteries are somewhat smaller than BCI Group 27 batteries and, if required, they can fit the battery compartments intended for group 27 batteries. But, due to the larger size, group 27 batteries feature better performances than group 24 batteries, at least regarding deep cycle applications.

Also, group 27 batteries can fit battery compartments intended for BCI Group 31 batteries, just be aware that due to the larger size, BCI Group 31 batteries are more powerful and feature larger capacities in general.

Note: whenever replacing any battery (not just Group 27 batteries), always be sure to check the actual size of the battery and the battery compartment. Although they fit in most situations, better safe than sorry.

The following comparison chart lists some of the most popular group 27 batteries, with their most important features and specifications:

Model Battery Type Cell Type
Capacity (Ah)
CCA MCA RC Weight Review
Banshee 27M Dual Purpose Enhanced Flooded 77 800 1000 140 51 lbs; 23.1 kg -
Banshee LFP-27M Dual Purpose LiFePO4 70 900 - ~165 18.8 lbs; 8.52 kg -
GreenLiFE Battery GL80-80AH Deep Cycle LiFePO4 80 - - - 28 lbs; 12.8 kg -
Mighty Max ML100-12 Deep Cycle AGM 100 - - - 63.9 lbs; 29 kg Mighty Max ML100-12
NorthStar NSB-AGM27F Dual Purpose AGM 92 930 1080 195 68 lbs; 31 kg -
NorthStar NSB-AGM27M Dual Purpose AGM 92 930 1080 195 68 lbs; 31 kg NorthStar NSB-AGM27M
Optima 8027-127 D27M Dual Purpose AGM 66 800 1000 140 54 lbs; 24.5 kg Optima 8027-127 D27M
Optima 8037-127 D27F Dual Purpose AGM 66 830 1000 140 54 lbs; 24.5 kg -
Renogy RBT100LFP12S-G1 Deep Cycle LiFePO4 100 - - ~200 26 lbs; 11.8 kg Renogy RBT100LFP12S-G1
UPG UB121000 Deep Cycle AGM 100 - - 170 64 lbs; 29 kg UPG UB121000
VMAXTANKS MR127-100 Deep Cycle AGM 100 - 800 200 68 lbs; 31 kg VMAXTANKS MR127-100
VMAXTANKS SLR-100 Deep Cycle AGM 100 - - 220 68 lbs; 31 kg -
VMAXTANKS XTR27-110 Deep Cycle AGM 110 660 880 220 68 lbs; 31 kg VMAXTANKS XTR27-100

Note: Amazon links open in the new windows ('Model' column), feel free to check them for the most up-to-date prices and offers.

As one can see, cranking-only group 27 batteries are not listed because they are very rare. Group 27 batteries are more than large enough that even the dual-purpose group 27 batteries are able to crank rather large diesel and especially gas engines - even some deep cycle models list both CCA (Cold Cranking Amps) and MCA (Marine Cranking Amps) values, suggesting that such deep-cycle batteries are versatile enough to be used for cranking of smaller engines, but with their main intended applications being deep cycle applications.

Dual-Purpose Group 27 Batteries

Dual-purpose group 27 batteries feature Cold Cranking Amps (CCA) in 800-930 Amps range, Marine Cranking Amps (MCA) in 1000-1080 Amps range, and feature Reserve Capacity (RC) in 140-195 minutes range.

Also, lead-acid dual-purpose group 27 batteries weigh between 51 and 68 pounds (~23.1 - 31 kg), while Lithium Iron Phosphate (LiFePO4) group 27 dual-purpose batteries weigh ~19 pounds (~8.5 kg).

optima d27m w300px

Although lithium batteries are more and more common on the market, dual-purpose group 27 batteries lithium batteries are not as common as group 27 deep-cycle lithium batteries.

Personally, if You are looking for a dual-purpose group 27 battery, go for a maintenance-free, spill-proof AGM battery, either NorthStar NSB-AGM27M or NSB-AGM27F (heavier, but stronger batteries with larger capacity) or go for Optima D27M or D27F (lighter, but somewhat weaker batteries).

Wet/flooded and enhanced-flooded group 27 batteries are still present on the market, offering certain benefits over AGM batteries, but personally, if You are looking for a lead-acid battery, go for an AGM battery. Just my 2c.

Deep-Cycle Group 27 Batteries

Deep-cycle group 27 batteries are not designed for cranking/starting applications - they are intended for deep discharge, cycle applications like off-the-grid applications, as trolling motor batteries, for electric vehicles, and similar.

mighty max ml100 12 1

Deep-cycle group 27 batteries feature a nominal capacity of 80-110 Ah, with Reserve Capacity of 170-220 minutes and weight of 64-68 pounds (29-31 kg) for AGM batteries and 26-28 pounds (11.8-12.8 kg) for lithium batteries.

The number of supported charging/discharging cycles often depends on the charging and discharging currents, the quality of the battery charger, and of course, on the Depth of Discharge percentage (DoD%) - while some models support up to 500 cycles down to 50% DoD, some models support up to 900 cycles down to 50% DoD (NorthStar group 27 batteries, for example).

Note: with the increase in performances, comes the higher price.

In order to check the actual performances of the batteries, the best thing to look for are constant current and constant power discharge charts, which are not always provided by the battery manufacturers.

One of the most popular general-purpose/deep-cycle group 27 batteries is the Mighty Max ML100-12 AGM battery.

Constant current discharge characteristics of the Mighty Max ML100-12 battery are given in the following chart (in Amps, at 77°F/25°C):

End Voltage Per Cell Battery End Voltage 10 min 15 min 30 min 45 min 1 hour 3 hours 5 hours 10 hours
1.60 V 9.6 V 207 162 92.0 66.5 53.5 24.0 16.2 9.20
1.65 V 9.9 V 195 154 89.3 65.1 52.5 23.5 16.0 9.15
1.70 V 10.2 V 183 145 86.4 63.6 51.3 23.0 15.7 9.10
1.75 V 10.5 V 170 136 83.2 62.0 50.0 22.5 15.4 9.05
1.80 V 10.8 V 155 126 80.0 60.0 48.5 21.8 15.0 9.00

Constant power discharge characteristics of the Mighty Max ML100-12 battery are given in the following chart (in watts, at 77°F/25°C):

End Voltage Per Cell Battery End Voltage 10 min 15 min 30 min 45 min 1 hour 2 hours 3 hours 5 hours
1.60 V 9.6 V 2250 1830 1032 750 618 372.0 280.8 189.0
1.65 V 9.9 V 2178 1734 1008 738 606 366.0 276.0 187.2
1.70 V 10.2 V 2100 1686 978 726 594 358.2 270.6 185.4
1.75 V 10.5 V 2010 1626 948 708 582 349.2 265.2 183.0
1.80 V 10.8 V 1890 1548 912 690 570 339.6 259.6 180.0

As one can see, when Mighty Max ML100-12 is being discharged for 20h, its (nominal) capacity is 100Ah, but when the battery is being discharged for only 1h, down to 10.5 volts, its actual capacity drops down to 51.3 Ah.

Such capacity drop is typical for an affordable, general-purpose AGM battery.

Premium AGM batteries usually feature 1h capacity in the range of 65-73% of 20h capacity, but sometimes they can cost 2-2.5x more than such affordable, general-purpose battery - if You don't mind having a somewhat heavier battery pack, it is sometimes more cost-effective to buy three 'cheaper' batteries than two 'premium' batteries and have a battery pack with better performances at the same price.

If the weight of the battery or battery pack is important, then go for either a premium AGM battery or for a lightweight, but even more expensive (at least initially) lithium battery.

rbt100lfp12s g1 table

Lithium batteries offer the same capacity but weigh 2-3x less than AGM batteries. If the batteries are being discharged in ~1h range, then the weight savings are even higher (3-5x) since the lithium batteries don't suffer from capacity drop like AGM batteries when the discharged current is being increased.

Also, lithium batteries can easily withstand 2000-5000+ charging/discharging cycles - in the long run, they are actually cheaper than AGM batteries.

But, lithium batteries feature Battery Management Systems that protect the batteries from unwanted events (overcharging, over-discharging, over- and under-temperature applications, etc.), with often limited currents, when compared with AGM batteries.

In most cases, the constant discharge current of the lithium batteries is ~1C - for example, a 100Ah lithium battery is able to withstand a 100 Amp discharge current.

Also, lithium batteries are able to provide short bursts of current, usually around 2C for 3-5 seconds, after which the current must drop below 1C or the BMS will disconnect the battery.

Of course, dual-purpose lithium batteries feature much stronger output currents than deep-cycle lithium batteries.

For short, due to the limitations of the built-in BMSs, and the differences between the BMSs of different lithium batteries, each model of lithium battery has its own features, so be sure to read the manual of such batteries thoroughly.

How to Charge Group 27 Batteries

Lead-acid group 27 batteries should be charged using smart AGM/Wet/Gel-Cell battery chargers that also feature charging modes like desulphation, cell equalization, and similar advanced features.

When such battery charger is connected to the battery, the battery itself is tested and the charging process is automatically adjusted to the battery's charge and its general condition.

Since group 27 batteries feature nominal capacity between 66 and 110 Ah, a good battery charger in the 15-30 Amps is recommended - actual charging current depends on the battery capacity and its ability to accept the charge.

Lithium group 27 batteries should be charged only with battery chargers intended for lithium batteries or with smart AGM battery chargers that feature dedicated charging mode for lithium batteries.

For example, if the lithium battery is being charged with AGM battery charger set to AGM battery, the charger may start the charging process with the battery desulphation (very short pulses of high voltage), which can either cause BMS to disconnect itself and the battery from the rest of the world or the BMS and battery can be, simply put - destroyed.

Group 27 Batteries as Trolling Motor Batteries

minnkota endura c2 mGroup 27 batteries can be used as very good trolling motor batteries, regardless of the trolling motor size/thrust.

Larger trolling motors with a maximum current draw of ~50 Amps can be powered for at least 1h with some energy left for safety.

Actual time depends on the battery capacity, its discharge characteristics, and of course, trolling style - if You are trolling most of the time at full throttle, then your trolling motor is too weak and the boat is underpowered.

If these batteries are used for kayaks, canoes, and similar smaller vessels with trolling motors using on average 25 Amps (RC value), then these batteries may provide power for 140-220 minutes, battery dependent.

If You need longer operating times for trolling, then consider either connecting more group 27 batteries in one battery pack or consider getting group 31 batteries or even 4D/8D batteries.

Group 27 Batteries as Sump Pump Backup Batteries

Sump pump batteries must operate reliably even after being for years in a standby mode - excellent role for the AGM group 27 batteries.

Sump pumps range in power from smaller 0.25 HP to much larger 1-2 HP (or even stronger) sump pumps, requiring from 20-22 Amps to hundreds of Amps, depending on the sump pump power and voltage - smaller sump pumps operate at 12V, while larger sump pump use 24, 36 or even 48 volts electric systems.

Another important feature of sump pumps is - starting current, which is not as high as the cranking current of the internal combustion engines, but it is often much higher than their operating current.

Because of these two requirements, long standby periods and higher initial current, lithium batteries are not suitable as sump pump batteries.

Most group 27 batteries are able to power 0.25 HP sump pumps (requiring 20-22 Amps) for up to 3 hours constantly (with some safety margin). But, due to the On/Off sump pump type of operation, actual time can be much longer, depending on the On/Off period ratio.

Of course, for stronger sump pumps, either go for premium group 27 batteries or go for larger group 31 batteries - it all depends on the individual needs and requirements.

 Group 27 Batteries as Power Inverter Batteries

With their deep cycle features and the ability to store plenty of energy, group 27 batteries are often used in off-the-grid applications as solar/wind batteries, or as power inverter batteries in emergencies and similar.

Typical general-purpose group 27 battery is able to power, for example, 12V 500W power inverter for ~1 hour constantly.

For example, a 500W power inverter with 85% efficiency, needs ~590 watts (~50 Amps @12 volts) of input power - most group 27 batteries are able to easily provide such power for 1 hour, without the voltage dropping below 10.5 - 10.8 volts, with the premium group 27 AGM batteries featuring even longer runtime.

On the other hand, lithium group 27 batteries are able to provide ~50 Amps for 1.5 - 2 hours, depending on the model. Also, lithium batteries are able to provide stronger currents when required by the power inverters for short periods of time.

If You need a power inverter battery that will cycle a lot, consider a lithium battery - in the long run, they are actually cheaper than AGM batteries, but also much lighter.

AGM group 27 batteries may be used for powering even stronger power inverters (1000W for example), but the capacity loss due to the strong discharge current is even larger.


Long Story Short: BCI Group 27 batteries are versatile batteries that are able to provide plenty of energy at the moment's notice and that can cycle a lot. Thus, they are commonly used in automotive, marine, and industrial applications.

When choosing 'the best' group 27 battery, always consider your own needs and requirements, since features and specifications of the batteries vary significantly:

Model Battery Type Cell Type
Capacity (Ah)
CCA MCA RC Weight Review
Banshee 27M Dual Purpose Enhanced Flooded 77 800 1000 140 51 lbs; 23.1 kg -
Banshee LFP-27M Dual Purpose LiFePO4 70 900 - ~165 18.8 lbs; 8.52 kg -
GreenLiFE Battery GL80-80AH Deep Cycle LiFePO4 80 - - - 28 lbs; 12.8 kg -
Mighty Max ML100-12 Deep Cycle AGM 100 - - - 63.9 lbs; 29 kg Mighty Max ML100-12
NorthStar NSB-AGM27F Dual Purpose AGM 92 930 1080 195 68 lbs; 31 kg -
NorthStar NSB-AGM27M Dual Purpose AGM 92 930 1080 195 68 lbs; 31 kg NorthStar NSB-AGM27M
Optima 8027-127 D27M Dual Purpose AGM 66 800 1000 140 54 lbs; 24.5 kg Optima 8027-127 D27M
Optima 8037-127 D27F Dual Purpose AGM 66 830 1000 140 54 lbs; 24.5 kg -
Renogy RBT100LFP12S-G1 Deep Cycle LiFePO4 100 - - ~200 26 lbs; 11.8 kg Renogy RBT100LFP12S-G1
UPG UB121000 Deep Cycle AGM 100 - - 170 64 lbs; 29 kg UPG UB121000
VMAXTANKS MR127-100 Deep Cycle AGM 100 - 800 200 68 lbs; 31 kg VMAXTANKS MR127-100
VMAXTANKS SLR-100 Deep Cycle AGM 100 - - 220 68 lbs; 31 kg -
VMAXTANKS XTR27-110 Deep Cycle AGM 110 660 880 220 68 lbs; 31 kg VMAXTANKS XTR27-100

Note: Amazon links open in the new windows ('Model' column), feel free to check them for the most up-to-date prices and offers.

When replacing the batteries, stay safe, and if You are unsure how to replace them, ask for professional help - better safe than sorry.