Optima D34M, D27M, D31M BlueTop Dual Purpose Marine Batteries are three models of very popular Optima AGM batteries. They are 'true' dual purpose batteries suitable as marine cranking batteries and deep cycle marine batteries. And they come at affordable price.

optima d34m d27m d31m 1

Depending on their intended purpose, Optima batteries in general come in three versions (actually four), easily distinguished by their top color: RedTop (automotive - starting), YellowTop (automotive - dual purpose) and BlueTop (dark gray top color - starting/cranking batteries and light gray top color - dual purpose/deep cycle batteries).

For more about version differences, please check Optima RedTop, YellowTop, BlueTop Batteries - Comparison and Recommendation article.

Technical data of Optima D34M, D27M, D31M BlueTop batteries is given in the following table:

Model Dimensions (LxWxH inches) Weight Capacity CA/MCA CCA RC RC Weight Ratio
8016-103 D34M BlueTop 10.06 x 6.88 x 7.94 43.5 lbs 55 Ah 870 A 750 A 120 min 2.76 min/lbs
8027-127 D27M BlueTop 12.19 x 6.81 x 8.75 53.8 lbs 66 Ah 1000 A 800 A 140 min 2.60 min/lbs
8052-161 D31M BlueTop 12.81 x 6.56 x 9.38 59.8 lbs 75 Ah 1125 A 900 A 155 min 2.06 min/lbs

Note: Battery links in the table are Amazon affiliate links. Batteries in the table are sorted according to their 20h capacity.

Optima BlueTop dual purpose batteries are known for their vibration resistance, they are spill-proof and can be mounted in any position, can be fully discharged/recharged many times etc.

Note: when discharging your lead-acid batteries (all AGM, Gel Cell, wet cells - not just Optima batteries!), don't discharge them below 20-25%. Modern smart battery controllers can prolong battery life by desulfating deeply discharged battery first and equalizing cells before floating charging phase, but don't abuse your batteries and they will serve you for a long time!

Optima BlueTop Dual Purpose Batteries Starting Current

Dual purpose batteries can't provide as large staring currents as purposely built starting batteries.

For example, if we compare Optima 34M BlueTop battery (dark gray casing, blue top - starting marine battery) with Optima D34M BlueTop battery (light gray casing, blue top - true dual purpose battery), we get:

Model Dimensions (LxWxH inches) Weight Capacity CA/MCA CCA RC RC Weight Ratio
Optima D34M BlueTop 10.06 x 6.88 x 7.94 43.5 lbs 55 Ah 870 A 750 A 120 min 2.76 min/lbs
Optima 34M BlueTop 10.06 x 6.88 x 7.94 38.4 lbs 50 Ah 1000 A 800 A 100 min 2.60 min/lbs

Note: Battery links in the table are Amazon affiliate links - feel free to check them for more reviews and recommendations.

optima bluetop darkgray starting batteryAs one can see, there is only one letter difference in the name of the batteries and they are so much different:

- Optima D34M - 'D' stands for 'deep cycle', '34' is for group size, and 'M' for marine operations (including recreational and other vehicles)

- Optima 34M - 'D' is missing since it is starting battery for marine, recreational vehicles and other similar applications.

For short - pay attention to that 'D' letter, when buying Optima deep cycle batteries! Photo on the right - Optima 34M battery - note the dark grey casing, typical color for Optima's starting batteries.

Optima D34M and 34M have the same physical dimensions, but 34M is ~5 pounds (~2.3 kg) lighter. Optima 34M can provide larger starting currents, regardless of the temperature. However, when drained at lower rate, D34M performs better - it has higher reserve capacity (RC - 120 min vs 100 min) and 20h capacity (55 Ah vs 50 Ah). Although it is heavier, RC weight ratio of D34M is better when compared with 34M (2.76 min/lbs vs 2.60 min/lbs).

Also, being true deep cycle battery, D34M can be regularly charged and discharged to about 20-25% of its capacity, without shortening its operating life, while 34M is simply not designed for cyclic use and should not be used as such.

It is needless to say that D34M costs more than 34M battery.

For short, if you need good starting battery that is resilient to vibrations, it is maintenance free, can operate in any position, sturdy and durable - go for Optima 34M BlueTop. For cyclic use, requiring good starting power, go for Optima D34M.

Optima BlueTop Dual Purpose Batteries Reserve Capacity

optima d31m bluetopIn the VMAXTANKS Batteries V30-800, V35-857, MR96, MR107, SLR125, MR137, SLR155 and MR197 Comparison article, we have compared VMAXTANKS MR137 deep cycle/dual purpose battery with Optima D31M 'true' dual purpose battery, since they both belong to the same BCI group - 31.

Optima D31M is lighter, cheaper and can provide larger starting currents. However, VMAXTANKS MR137 is more optimized for lower discharging currents and have higher RC and 20 Ah capacity.

Note: it is perhaps not fair to compare batteries taking their BCI group size as a starting point, but we have to start somewhere, right? :)

If we compare Optima BlueTop batteries, although D34M is the smallest of them all, it is perhaps the best performer of them all. For example, if we compare the batteries by weight, we get:

- D34M - 1.26 Ah/lbs, 20 MCA A/lbs, 17.2 CA A/lbs, 2.76 RC min/lbs,

- D27M - 1.22 Ah/lbs, 18.58 MCA A/lbs, 14.87 CA A/lbs, 2.60 RC min/lbs,

- D31M - 1.25 Ah/lbs, 18.81 MCA A/lbs, 15.05 CA A/lbs, 2.06 RC min/lbs.

Obviously, D27M and D31M are fine dual purpose marine batteries, but D34M is excellent.

Note: If you do require dual purpose battery which has to supply, for example, 600-700 cranking Amps, or it must supply 25A for 90-100 minutes on regular basis, or even both, personally, I would go for D27M, or even for D31M battery - they are heavier, but it is good to have some power/energy reserve (call me paranoid, but ...). Also, if found on sale, D27M can be even cheaper than D34M and 10.3 lbs weight and some size difference is not issue for me.

For somewhat less demanding applications, go for D34M battery, and don't look any further.

Optima D34M Dual Purpose Marine Battery vs. VMAXTANKS MR96-60 Deep Cycle Battery

In this article, we have compared starting abilities of Optima D34M battery with Optima 34M battery.

Now, we are going to compare Optima D34M with VMAXTANKS MR96-60 deep cycle battery. Their technical data is given in the following table:

Model Dimensions (LxWxH inches) Group Size Weight Capacity CA/MCA CCA RC RC Weight Ratio
Optima D34M BlueTop 10.06 x 6.88 x 7.94 34 43.5 lbs 55 Ah 870 A 750 A 120 min 2.76 min/lbs
VMAXTANKS MR96-60 9.2 x 5.5 x 8.2  22NF  43 lbs 60 Ah 600 A - 120 min 2.79 min/lbs

Although these batteries don't belong to the same BCI group, they are very similar - MR96-60 is shorter and narrower, but also taller little bit. D34M is half a pound (~0.22 kg) heavier - their weight difference is within 1%.

CA - Cranking Amps: Optima D34M can provide 870 CA Amps, while VMAXTANKS can provide 600A - that is 270 A difference, almost 50% in favor of D34M.

CCA - Cold Cranking Amps: Optima D34M can provide 750 Amps, while there is no official data for MR96-60. Luckily, this value can be easily calculated:

CCA = MCA x 0.80 = 600 x 0.80 = 480 Amps

This formula is not exact and it depends on battery chemistry, design and model. However, it is good enough to compare these batteries - 750 CCA Amps of D34M is by far better than 480 Amps of MR96-60.

HCA - Hot Cranking Amps: There is no official data for HCA of the Optima D34M battery. However, it can be approximately calculated, too:

HCA = CCA x 1.66 = MCA x 1.33

HCA = 750 x 1.66 = 1245 Amps (calculated from Cold Cranking Amps!)

HCA = 870 x 1.33 = 1157 Amps (calculated from Cranking Amps!)

That is on average 1200 HCA Amps for Optima D34M battery - if we find official HCA value of this battery, we will update this article right away!

 VMAXTANKS MR96-60 can provide 1150 HCA Amps (official data from VMAXTANKS web site).

optima d34m bluetopAlthough we can't compare actual CCA and HCA data of these batteries, it appears (meaning, we are not 100% sure due to lack of official data) that as temperature rises, advantage of D34M battery declines in terms of starting current.

Capacity - these batteries are equal in term of Reserve Capacity (RC) and can supply 25 Amps of current for 120 minutes. However, when discharged slowly, MR96-60 performs better - when they are drained for 20h, MR96-60 has 60 Ah capacity (supplies 3 A for 20h) and D34M has 55 Ah capacity (supplies 2.75 A for 20h). Not big difference, but worth mentioning.

Long story short - if you need deep cycle battery for low currents (less than 3 Amps), for example, for fish finder or similar, MR96-60 is better choice.

If you do need trolling battery for applications that consume more than 25 Amps and still must be able to start the internal combustion engine, Optima D34M is better choice.

For applications that use between 3 and 25 Amps, these two batteries are practically equal.


Battery links in this article are Amazon affiliate links and if You use them and in the end You buy something from Amazon, it is fair to say that we get a commission, which helps this site running :)

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