BCI Group 31 Batteries

BCI Group 31 batteries are very popular automotive, marine and industrial batteries, designed as deep cycle and dual-purpose batteries, and intended for standby/float and cycling applications where strong batteries with sufficient capacities are required.

BCI Group 31 batteries are generally sealed lead-acid (SLA) Absorbent Glass Mat (AGM) and Gel-Cell batteries, but with the improvements in technology lithium-ion batteries are becoming more and more popular.

odyssey 31m pc2150 w300px

BCI Group 31 Batteries Features and Specifications

BCI Group 31 batteries physical dimensions are (L x W x H) 13 x 6 13/16 x 9 7/16 inches (13 x 6.8125 x 9.4375 inches, 330 x 173 x 240 mm), with the positive battery terminal on the left side, when the battery is being viewed from the front.

Battery terminals vary depending on the intended use, but generally, they are automotive terminals, marine terminals, and 'ordinary' bolt terminals (M8 for example).

When ordering any battery, not just BCI Group 31 battery, always check the actual size of the battery, its terminals type and orientation, battery chemistry, and other specifications.

Note: there are several BCI battery groups that are very similar in size to the BCI Group 31 batteries:

- Group 27: 12.0625 x 6.8125 x 8.875 inches (306 x 173 x 225 mm),

- Group 30H: 13.5 x 6.8125 x 9.25 inches (343 x 173 x235),

- Group 31: 13 x 6.8125 x 9.4375 inches (330 x 173 x 240 mm).

Group 27 and Group 31 are very popular battery groups, while Group 30H is present on the market, but not that much. Also, some of the Group 30H batteries are, although officially labeled as Group 30H batteries, actually Group 31 batteries.

BCI Group 31 Batteries Comparison Chart

The most popular dual-purpose and deep cycle group 31 batteries, with their most important features and specifications, are given in the following comparison chart:

Model Battery Type Cell Type Ah CCA MCA RC Weight (lbs/kg)
Absolute UX121100 Dual Purpose AGM 110 773 1005 190 65.5 lbs; 29.7 kg
AIMS Power LFP12V100A Deep Cycle LiFePO4 100 - - ~240 30.2 lbs; 13.7 kg
Ampere Time LFP-12V-100Ah-A1 Deep Cycle LiFePO4 100 - - ~240 25.4 lbs; 11.5 kg
Banshee 31M Dual Purpose Enhanced Flooded 105 800 - 190 52.6 lbs; 23.9 kg
Battle Born 100Ah 12V LiFePO4 Deep Cycle LiFePO4 100 - - ~240 29 lbs; 13.2 kg
Exide XMC-31 Deep Cycle AGM 100 925 1110 200 68 lbs; 31 kg
ExpertPower EP12100 Deep Cycle LiFePO4 100 - - ~240 29.7 lbs; 13.5 kg
GreenLiFE Battery GL100 Dual Purpose LiFePO4 100 - - 240 28 lbs; 12.7 kg
Interstate DCM0100 Deep Cycle AGM 110 - - - 64.9 lbs; 29.4 kg
Lifeline GPL-31T Deep Cycle AGM 105 600 750 195 69 lbs; 31.5 kg
Lifeline GPL-31XT Deep Cycle AGM 125 650 800 230 69 lbs; 31.5 kg
Lifeline GPL-3100T Dual Purpose AGM 100 810 950 228 67 lbs; 30.4 kg
LiONCore VPW-551116 Deep Cycle LiFePO4  100 - - ~240 30.8 lbs; 14.0 kg
Mighty Max ML12-100 Deep Cycle AGM 100 - - <180 63.9 lbs; 29.0 kg
NorthStar ELT-AGM31 Dual Purpose AGM 100 925 1050 190 65.7 lbs; 29.8 kg
NorthStar NSB-AGM31 Dual Purpose AGM 103 1150 1370 220 75 lbs; 34.0 kg
NorthStar NSB-AGM31M Dual Purpose AGM 103 1150 1370 220 75 lbs; 34.0 kg
Odyssey 31M-PC2150 Dual Purpose AGM 100 1150 1370 205 77.8 lbs; 35.3 kg
Optima 8052-161 D31M Dual Purpose AGM 75 900 1125 155 59.8 lbs; 27.1 kg
Renogy RNG-BATT-AGM12-100 Deep Cycle AGM 104 - - 180+ 66 lbs; 29.9 kg
Renogy RNG-BATT-GEL12-100 Deep Cycle Gel 100 - - 180+ 60 lbs; 27.2 kg
Renogy RBT100GEL12-G1 Deep Cycle Gel 100 - - ~175 63.9 lbs; 29 kg
Trojan T31-AGM Deep Cycle AGM 102 - - 200 70 lbs; 31.7 kg
VMAXTANKS SLR125 Deep Cycle AGM 125 - - 260 75 lbs; 34 kg
VMAXTANKS MR137-120 Deep Cycle AGM 120 - 900 230 75 lbs; 34 kg
VMAXTANKS VPG12C-100LFP Deep Cycle LiFePO4 100 - - ~240 26.4 lbs; ~12.0 kg
VMAXTANKS XTR31-135 Deep Cycle AGM 135 730 920 265 77 lbs; 34.9 kg
XS Power XP3000 Deep Cycle AGM 120 - - 240 73 lbs; 33.1 kg
Weize 12V 100Ah AGM Deep Cycle AGM 100 - - - 60 pounds; 27.2 kg
Weize 12V 100Ah Gel Deep Cycle Gel 100 - - <180 67 pounds; 30.4 kg
WindyNation BAT-NSAP12-100 Deep Cycle AGM 106 - - 180+ 67 lbs; 30.4 kg

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

The most popular lead-acid group 31 batteries are AGM batteries, although there are several excellent deep-cycle Gel-cell batteries as well.

Lithium group 31 batteries are Lithium Iron Phosphate (LiFePO4) batteries, almost exclusively designed as deep-cycle batteries.

Lead-Acid Group 31 Batteries

Lead-acid group 31 batteries are sealed AGM and Gel-Cell deep-cycle and dual-purpose batteries.

Note: there is no dedicated starting group 31 battery for a very simple reason - dual-purpose group 31 batteries are large enough to be able to easily provide high-cranking currents, required for starting large diesel and petrol engines.

northstar nsb agm31 w300px

Deep-cycle group 31 lead-acid batteries feature a nominal capacity of 100-135 Ah, Reserve Capacity of 170-265 minutes and they weigh between 60 and 77 pounds.

Depending on the internal design, these batteries may withstand 250-350 cycles down to 90-100% DoD and 500-600 cycles down to 50-80% DoD. Of course, these values differ.

Note: number of cycles depends on the quality of the battery, which in the end dictates the price of the battery.

Dual-purpose group 31 lead-acid batteries feature a nominal capacity of 75-103 Ah, Reserve Capacity of 155-220 minutes and they weigh between 60 and 78 pounds.

While deep-cycle batteries are often made as general-purpose, budget-friendly batteries, dual-purpose group 31 batteries are very often made as high-quality, industrial batteries that are often used in marine and automotive applications.

As such, dual-purpose batteries feature Cold Cranking Amps (CCA) values up to 1150 Amps, Marine Cranking Amps (MCA) values up to 1370 Amps and they often tolerate even more deep discharge cycles than the deep-cycle batteries.

But, premium dual-purpose group 31 batteries do come with a very 'nice' price tag.

optima d31m w300px

How to charge lead-acid group 31 batteries?

When they are part of an electric system consisting of an internal combustion engine and alternator designed for charging such batteries, the best course of action is to let the built-in system charge the battery.

When the battery is being charged outside of any such system, it is recommended to charge the battery with an intelligent lead-acid battery charger that supports the charging of flooded/AGM/Gel float/cycling batteries.

Such battery chargers analyze the battery first and only then charge the battery according to its condition.

Most group 31 batteries may be recharged with battery chargers with a maximum charging current in the 15-25 Amps range.

For example, 15 Amps battery charger may recharge 100Ah battery discharged down to 50% DoD in less than 4 hours.

Lithium Group 31 Batteries

Lithium group 31 batteries are almost exclusively deep-cycle batteries, being able to withstand 2000-4000 cycles down to 100% DoD and often more than 7000 cycles down to 50-80% DoD.

Although lithium group 31 batteries initially cost more than lead-acid batteries, considering the number of supported cycles, lower weight (2-3x lighter), faster recharging, and similar, no wonder that deep-cycle LiFePO4 batteries are gaining in popularity, especially for applications where batteries are discharged with 50-100 Amps currents, where battery weight is of an issue and where the battery is required to cycle a lot.

Note: 100Ah lead-acid battery features 100Ah capacity when being discharged for 20h. When 100Ah lead-acid battery is being discharged with constant current for one hour, its actual capacity drops down to ~55-72% of its nominal capacity. Lithium batteries often feature a 1h capacity which is at least 95-98% of their 5h (nominal) capacity.

greenlife gl100 w300px

GreenLiFE GL100 battery is a lithium battery that is labeled as a dual-purpose battery.

Note: don't mix GreenLiFE GL100 group 31 battery and GreenLiFE GL100M group 24 battery - they are both 100Ah lithium batteries, but they differ in size and shape.

GreenLiFE GL100 lithium battery is designed as a 'drop-in replacement' for flooded, AGM, and Gel-Cell batteries and is able to provide 1000 Amps for 5 seconds, unlike most group 31 batteries which are able to provide 150-200 Amps for 3-5 seconds.

Thus, GreenLiFE GL100 may be used even as starting/cranking battery and as a deep-cycle battery, since it supports up to 3000-5000 charging/discharging cycles.

Generally, 100Ah lithium batteries feature maximum continuous discharge current in the 80-100 Amps range, GreenLiFE GL100 battery included.

expertpower ep12100 w300px

How to charge lithium group 31 batteries?

Lithium group 31 batteries designed as 'drop-in replacements' for automotive/marine applications may be charged via built-in alternators just as lead-acid batteries.

However, when being charged outside such systems, lithium batteries should NOT be charged with intelligent AGM battery chargers that feature desulphation/equalization and similar charging modes required for AGM batteries.

Lithium batteries should be charged using DEDICATED lithium battery chargers or AGM battery chargers that feature dedicated lithium battery charging modes.

Such battery chargers/modes charge lithium batteries using the CC/CV (Constant Current/Constant Voltage) charging algorithm, which is optimized for lithium batteries.

Most 100Ah lithium batteries feature a maximum continuous charging current of 30-50 Amps, so 20-25 Amps lithium battery chargers are recommended.

For example, a dedicated 20 Amps lithium battery charger can recharge 100Ah battery discharged down to 50% DoD in less than 3 hours.

Long Story Short: General-purpose, deep-cycling lead-acid group 31 batteries are budget-friendly batteries excellent for various standby and cycling, low to medium current applications.

odyssey 31m pc2150 w150pxPremium dual-purpose AGM batteries are strong, robust, and reliable batteries designed for both starting/cranking and deep cycle applications and applications under the most severe, cold weather.

Lithium group 31 batteries are initially expensive, but considering their excellent discharge characteristics, huge number of charging/discharging cycles, and lightweight design, they are in the long run actually cheaper than lead-acid batteries. Just be sure to charge them properly.