Group 27 vs. Group 29 vs. Group 31 Battery – Which One Is The Best?

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Are you looking to get a new battery for your car, RV, or motorboat? If you are, then you’ve come to the right place.

You haven’t far to go before you can choose the right battery group size available. All you now have to do is select the one that meets your needs the best.

This article will provide a little more information relating to Group 27, Group 29, and Group 31 batteries.

Group 27 vs. Group 29 vs. Group 31 Battery: What Are The Differences To Compare When Buying?

”Group size” doesn’t refer to a particular battery model but rather to the size of the battery, the location of the terminals. But be aware a higher number doesn’t mean a larger size battery case.

The significant differences between the batteries we discuss in this article relate to their physical size and their storage capacity.

By now, you are aware batteries come in a variety of different sizes. Many are given particular “group” sizes based on their physical size and placement of terminals. This isn’t anything to do with the battery’s actual energy capacity.

So let’s look closely at some of the fundamental differences related to Group 27, 29, and 31 batteries.

#1 Difference: Dimensions

 Group 27Group 29Group 31
Dimensions12×6.8×8.9 in13×5.5×8.9 in13×6.8×9.4 in
Dimensions306x173x225 mm330x140x227 mm330x173x240 mm
Terminal PositionsLeft-PositiveRight-PositiveLeft-Positive

It may surprise you to learn that the difference on paper between all 3 of these battery group sizes is not that much:

  • Group 27: 12×6.8×8.9 in
  • Group 29: 13×5.5×8.9 in
  • Group 31: 13×6.8×9.4 in

Group 27 vs. Group 29: There is a difference in length of 1″ and width of just 1/2”.

Group 29 vs. 31 batteries: They are very similar in size, although the 31 batteries are a little larger than the 29. The crucial difference between these 2 batteries is that the Group 31 one is slightly taller than the Group 29 model.

#2 Difference: Weight

The difference in weight between these 3 types of Group batteries is something you need to know. How much each one weighs depends on how they have been constructed.

  • Group 27 battery weight can range from 54 to 70 pounds
  • As for a Group 29, these can weigh between 50 and 65 pounds.
  • Group 31 batteries, typically, can weigh between 60 and 75 pounds.

However, if metal lithium has been used to construct these batteries, they can weigh even less. In fact, for Group 29 and 31 batteries, these can weigh no more than 25 to 30 pounds.

#3 Difference: Storage Capacity – Check The Storage Capacity With RC Rating Or Ah Rating

The storage capacity between each of these batteries is very significant.

Be aware that the bigger the battery then the more lead plates it has installed. This means that it has a much greater charge storage capacity. As a result of this, it can hold a charge for much longer meaning it will keep any electronics running off of it working for longer.

RC Rating

A battery’s RC rating relates to its repetitive reserve capacity. This is a significant battery rating as it tells you just how many discharge/recharge cycles it can withstand. Yet it can still deliver a charge that relates to its original total capacity.

  • Group 27 models these come with between 140 to 220 minutes of RC.
  • Group 29 models these batteries have an RC rating of between 190 and 220 minutes.
  • Group 31 batteries have an RC of between 155 and 240 minutes.

So their RC rating really isn’t all that different. But it would help if you are looking for batteries with a high RC rating as these can be completely drained and fully recharged a lot more.

Ah Rating

When it comes to the Ah rating on a battery, it will tell you the total number of amps they can produce over 20 hours. So a battery with a 100-amp rating can have 5 amps per hour over 20 hours.

Like the RC rate, Ah is a measure of capacity but quantified using different discharge rates. It’s simple to understand that the RC is always almost twice the Ah rate.

Ah= (RC: 2) + 16

The actual time that any of these batteries will last depends on how much it is used. Again size doesn’t always mean that they are going to provide power for longer.

#4 Difference: CCA Rating

All batteries, even the true deep cycle variety, comes with a CCA rating. All this means is that it shows you just how much current can be drawn from the battery when it is cold for a certain amount of time.

CCA (cold cramping amps) shows just how much energy can be dumped in one go, such as when you start your car. Some batteries come with a high CCA but have a low RC. While others have a high RC but a low CCA.

  • Group 27 batteries: 600 – 1,000 CCA.
  • Group 29 batteries: 650 – 900 CCA.
  • Group 31 batteries: 600 – 1,150 CCA.

So again, the difference in their CCA ratings is relatively minimal.

Can I Use A Different Group Size Battery?

We would recommend that you have one that is based on the actual size of the box where the battery will be sitting. You could, of course, install the largest battery that fits into the box in your vehicle.

If you choose to do this, be aware that you have to modify the brackets that hold the battery in place. Also, any additional tongue weight means that you may need to replace the box altogether.

So if the battery box in your vehicle is specifically for a Group 27 battery, then you’ll find that neither a Group 29 nor 31 one will fit into this space. To upgrade to, say, a Group 31 battery will require not only replacing the battery box.

You will also need to cut the opening underneath to make it bigger for the new battery box to be installed.

Therefore, make sure that any of the Group 29 or 31 batteries you are considering installing will fit in the space available.

Is It Worth Switching To Group 29/Group 31 Battery?

In answer to this question, yes, switching over to Group 29 or 31 batteries is a good idea. The first reason being that these batteries come with a longer warranty, and the second is that they have more power.

However, you really should only consider switching over to such batteries based on your particular needs and if your budget allows for it.

Car Battery Recommendations Based on Group Size

At a glance: Top 5 Picks for Group 27, Group 29 and Group 31 Batteries

Universal Group 27Universal Group 27
  • Size: 12.17x6.6x9.16 in
  • Capacity: 100 Ah
  • RC: 180 mins
  • Supported vehicles: off-grid applications, travel trailers
Check Price
Optima BlueTop Group 27Optima BlueTop Group 27
  • Size: 12.2x6.8x8.7 in
  • Capacity: 66 Ah
  • RC: 140 mins
  • Supported vehicles: boats, RVs, trolling motors


Check Price
VMAX Group 27VMAX Group 27
  • Size: 12.1x6.7x8.2 in
  • Capacity: 100Ah
  • RC: 260 mins
  • Supported vehicles: RVs, campers, golf buggies 
Check Price
VMAX MR137-120 Group 31VMAX MR137-120 Group 31
  • Size: 13x6.8x8.8 in
  • Capacity: 120 Ah
  • RC: 230 mins
  • Supported vehicles: boats, trolling motors
Check Price
Renogy Group 31Renogy Group 31
  • Size: 13.1x6.9x8.6 in
  • Capacity: 100 Ah
  • RC: 240 mins
  • Supported vehicles: RVs, campers, off-grid applications
Check Price
VMAX SLR125 group 31VMAX SLR125 group 31
  • Size: 12.9x6.8x8.7 in
  • Capacity: 120 Ah
  • RC: 260 mins
  • Supported vehicles: medium-sized motorboats, RVs, campers
Check Price

Best Group 27 Batteries

Of the various Group 27 batteries now available, the 3 we would recommend you consider purchasing are:

Battery With The Lowest Cost Per Minute Of RC: Universal Power UB121000

Universal Power UB121000
Universal Power Group 27 Battery
It’s a battery for deep cycle applications: fridge, audio, fan, etc. The cost of about $170 will be what attracted you to it in the first place, and you will never regret, a great price for what you get.

This Battery measures 12.17 x 6.61 x 9.16 inches and weighs in at over 63 lbs. For such a reasonable-sized battery, it can provide power for up to 180 minutes.

There are many applications where such a battery can be used. Not only is it suitable for use on a wide range of boats that have either gas or diesel engines. It is also good for providing power in RVs.

Honorable Mention: Optima D27M

Optima D27M
Optima BLUETOP D27M Battery
Optima D27M brings your vehicle the best value for trouble-free long life. This battery can take more vibration than a regular battery, which is suited to marine use as it won’t leak under rough conditions.

This battery measures 12.2 x 6.8 x 8.7 inches and weighs in at just 25lbs. As you should expect for a battery of this size, it has a reserve capacity of up to 140 minutes.

Even though this is one of the smallest batteries, we recommend it still has enough power to provide energy to high-demand electronics on boats. Along with sufficient power to provide energy to bilge pumps, fish finders, GPS systems, and a stereo, it also provides enough power to start the boat’s engine.

Best Reserve Capacity Battery: VMAX SLR100

VMAX SLR100 Group 27 Battery
Made in the USA, VMAX SLR100 is much better than other cheap lead acid batteries on the market. It not only perfectly fits your Group 27 battery box but provides 100Ah to withstand the most demanding applications.

This battery measures 12.1 x 6.7 x 8.2 inches and weighs 67 lbs. It also has an RC (reserve capacity) of 260 minutes.

As well as being suitable for use daily can also provide you with backup power. Especially good to be used in vehicles such as RV’s and campers and golf buggies or mobility vehicles. Also great for giving energy to small powerboats as well as jet skis and other small marine vehicles.

Best Group 29 Batteries

As you will discover, there are many Group 29 batteries now available, but the ones we would recommend to you are:

Best Reserve Capacity Battery: EverStart Maxx Marine Battery

This battery measures 13 x 6.8 x 10 inches and weighs in at 61 lbs. It can provide power for anywhere up to 205 minutes.

This battery is designed for use in small to medium-sized motorboats and provides power to jet skis and snowmobiles. It can provide energy to all onboard electrical systems and trolling motors as able to produce a stable stream of power.

Find the best purchasing options for more Group 29 Batteries at Amazon here.

Honorable Mention: Interstate Battery SRM-29

This Battery measures 13 x 6.75 x 10 inches and weighs in at 59 lbs. This Battery from Interstate has a reserve capacity of up to 210 minutes.

As with other batteries in this article, we recommend using this one to provide power to the electrical systems on small or medium-sized boats. It is also suitable for use to provide power to jet skis, campers, and RV’s.

RELATED: Best Interstate Battery Review 2021 [Are these worth the money?]

Best Group 31 Batteries

Again there are quite a few different Group 31 batteries to choose from made by different manufacturers. The ones that we recommend you consider are shown below.

VMAX MR137-120 AGM Battery

VMAX MR137-120
VMAX MR137-120 Group 31 Battery
VMAX MR137-120 gives a great value compared to its competitors. With the Ah rate of120 Ah, it can have enough storage power for running your boats, trolling motors, vans all day.

This battery is slightly larger than the above model measuring 13 x 6.8 x 8.8 inches, and yet weighs the same at 75 lbs. This battery comes with a reserve capacity of up to 230 minutes.

VMAX MR137 is designed to provide power to appliances on a boat, such as trolling motors. It also provides power to other electrical equipment on a ship that has a heavy power load. Plus, it can provide sufficient power to provide energy to vehicles such as campers and RV’s.

Honorable Mention: Renogy Deep Cycle AGM Battery

Renogy 100 Ah Battery
Renogy 100Ah Group 31 Battery
This is a monster of a battery that is perfect for indoor uses, van life, RV, etc. without releasing toxic gases. Amazing customer service is a plus for this Renogy product.

This Battery by Renege measures 13.1 x 6.9 x 8.6 inches and weighs a total of 63.9 lbs. Like other similar-sized batteries, this one has an RC of up to 240 minutes.

Renege battery can be used to provide both stand-by power and power on a daily basis. It is excellent for use in various vehicles such as RV’s, campers, and boats. It also is great to use in off-the-grid solar power systems.

Battery with the lowest cost per minute of RC: VMAX SLR125 AGM Battery

VMAX SLR125 125 Ah Group 31 Battery
VMAX SLR125 has the outstanding performance to provide additional power to solar systems. It’s the best battery available to withstand the most demanding solar applications.

As already mentioned above, this battery measures 12.9 x 6.8 x 8.7 inches and weighs 75 lbs. With a reserve capacity of up to 260 minutes, it is one of the most cost-effective models to buy.

VMAX SLR125 is suitable to use for providing power in small to medium-sized motorboats. It is also suitable for use in both RV’s and campers.


What’s The BCI Code?

These days, typically, the BCI codes are used when it comes to batteries for placing them in groups U1, 24, 27, 29, and 31.

What’s A Battery’s Designated Part Number?

When it comes to industrial batteries, these also come with a designated part number, for example, “GC” for golf cart and “FS” for floor sweeper.

Other standard size codes are used relating to the larger industrial batteries that are most commonly used in solar electric systems. The codes designated for these batteries are 4D and 8D.

How many CCAs do I need?

How much CCA you require does depend on the size and type of engine in your vehicle. For example, if your vehicle has a diesel engine, it needs a higher CCA rating, as these can be harder to start when the engine is cold.

It also depends on the engine oil viscosity, circuit resistance, accessory loads, and external temperature. In colder climates, the batteries require a higher CCA rating. This will help to ensure that starting your vehicle on a cold winter’s morning is much easier.

But at the end of the day, you should go on what the manufacturer of your vehicle is recommending.

What Battery Brands To Buy?

It is important to note that just three manufacturers make most auto batteries. These are Delphi, Exide, and Johnson Control Industries.

Also, it is essential to remember that they then sell these batteries under several different brand names.

  • Delphi makes ACDelco and EverStart (Walmart) Group batteries.
  • Exide is the maker of Exide, Champion, Napa, and some EverStart Group batteries.
  • As for Johnson Controls Industries, the brands they make are Duralast for AutoZone, Diehard for Sears, Kirkland for Costco, Motorcraft for Ford, EverStart, and Interstate models.

With so many models to choose from, how do you decide which brand you should buy?

It is a good idea to choose a brand of battery manufacturer that you recognize.

Also, take a close look at the kind of warranty they offer. Go with a brand that offers you the most extended full replacement term. Some manufacturers offer only a 12-month warranty to replace the battery for free, while others offer much longer.

Finally, look closely at the kind of customer support they provide. If you were to have any problems, how quickly will they deal with the situation?

How To Choose Which Group Battery Based On Ah Rating?

The first thing you should know is that you will only use 50% of your Battery’s Ah rating. This means that if the battery you’ve chosen comes with a 100Ah rating, you can only use 50Ah of this.

To choose a battery based on its Ah rating, you need to work out how much power you’ll need. This is important if you are going to be running everything solely on the battery.

We hope the information that I’ve provided with you above will help you ensure that you buy the right kind of Group battery for your vehicle. Please let me know what you think by leaving a comment below.

RELATED: Group 24 vs. 34 Battery – Which One Should You Get?

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