Optima D34M, D27M, D31M BlueTop Dual Purpose Marine Batteries
Optima D34M, D27M, and 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 an affordable price.
Updated: December 8, 2022.
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Intro To Optima BlueTop Dual Purpose Batteries
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, and 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 |
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Optima BlueTop dual-purpose batteries are known for their vibration resistance, they are spill-proof and can be mounted in any position except upside down, 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 batteries first and equalizing cells before the floating (maintenance) 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 starting currents as purposely built starting batteries.
For example, if we compare the Optima 34M BlueTop battery (dark gray casing, blue top - starting marine battery) with the 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 |
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As one can see, there is only one letter difference in the name of the batteries, but they are so much different in many details:
- 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, dual purpose and/or starting 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 a lower rate, D34M performs better - it has a higher reserve capacity (RC - 120 min vs. 100 min) and 20h capacity (55 Ah vs. 50 Ah). Although it is heavier, the RC weight ratio of D34M is better when compared with 34M (2.76 min/lbs vs. 2.60 min/lbs).
Also, being a true dual-purpose 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, the D34M costs more than the 34M battery.
In short, if you need a good starting battery that is resilient to vibrations, is maintenance-free, can operate in any position except upside down, and is 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
In 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 - group 31.
Optima D31M is lighter, cheaper, and can provide larger starting currents. However, VMAXTANKS MR137 is more optimized for lower discharging currents and has 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 the following:
- 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 that has to supply, for example, 600-700 cranking Amps, or it must supply 25A for 90-100 minutes on a 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 are not an issue for me.
For somewhat less demanding applications, go for the Optima 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 the Optima D34M battery with the 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 |
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Although these batteries don't belong to the same BCI group, they are very similar - MR96-60 is shorter and narrower, but also a 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 a 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 the calculated 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 the Optima D34M battery - if we find the official HCA value of this battery, we will update this article immediately!
VMAXTANKS MR96-60 can provide 1150 HCA Amps (official data from VMAXTANKS website).
Although 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, the advantage of the D34M battery declines in terms of starting current.
Capacity - these batteries are equal in terms 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 discharged for 20h, MR96-60 has 60 Ah capacity (provides 3 A for 20h), and D34M has 55 Ah capacity (provides 2.75 A for 20h). Maybe this is not a big difference, but worth mentioning.
How To Charge Optima BlueTop Dual-Purpose Marine Batteries
When Optima BlueTop batteries are connected to the electric system of the boats, yachts, vehicles, and similar, the onboard alternator, in combination with the charge controller, charges the batteries.
However, when these batteries are charged at the workshop or garage, one should use intelligent AGM battery chargers/maintainers, which analyze the battery first and only then recharge the battery using the optimized charging algorithm.
Such battery chargers are able to desulfate the battery's plates, equalize the battery cells, and maintain the battery fully charged for a longer period of time.
Optima offers two suitable battery chargers, Optima 400 12V Digital Charger and Optima 1200 12V Digital Chargers, but any smart 5-10A 12V AGM battery charger will do fine.
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For example, when the Optima D34M BlueTop battery is discharged down to 20% SoC (State of Charge; 80% DoD Depth of Discharge; remaining capacity 11Ah), a good 5 Amps battery charger will recharge the battery in ~10 hours, while 10 Amps battery charger will recharge the battery in ~5 hours.
Frequently Asked Questions (FAQ)
Here are some of the most common Frequently Asked Questions (FAQ) about Optima BlueTop batteries and other batteries in general:
Which Optima battery do I need?
- This depends on your needs:
- If You are looking for starting/cranking batteries, go for RedTop batteries or BlueTop with a dark gray casing,
- If You are looking for dual-purpose or deep-cycle batteries, go for YellowTop batteries or BlueTop with a light-gray casing,
- If You are looking for a specific BCI battery group size, check the size that You need and verify if Optima offers such batteries.
Are Optima marine batteries worth it?
Generally, yes, Optima batteries, not just marine batteries, are worth it. Just be sure not to abuse them, at least not too much.
How long do Optima marine batteries last?
Depends on their use, charging, weather conditions, and similar. A good AGM battery lasts less than 2 years if not treated properly and sometimes 5+ years when used and maintained properly.
Which Optima battery for a 30A trolling motor?
Optima D31M has the highest capacity, and it is recommended as the largest Optima dual-purpose battery as a trolling motor battery for 30 Amps trolling motors.
What does a 1000 CCA battery mean?
A battery that features 1000 CCA (Cold Cranking Amps) is able to provide 1000 Amps battery for 30 seconds, with the voltage NOT dropping below 7.2V, at 0°F (-18°C).
Optima doesn't offer such dual-purpose marine batteries, but any two Optima BlueTop dual-purpose batteries connected in parallel can provide 1000+ Amps.
Note: when connecting batteries in parallel and series, it is highly recommended to use the very same battery models from the same battery manufacturer, preferably from the same batch.
Long story short: If You are looking for mechanical and vibration-resistant marine dual-purpose Absorbent Glass Mat (AGM) batteries that are able to withstand many charging/discharging cycles and are able to provide strong starting currents, consider Optima BlueTop dual-purpose marine batteries.
Thanks to their spiral-wound cells, Optima marine batteries are lighter than similar batteries with flat-plate cells but are nonetheless able to provide similar cranking/starting Amps.
Also, as trolling batteries, Optima BlueTop dual-purpose batteries are a good choice for smaller 20-30 Amps trolling motors, while for larger units, 100+Ah AGM and especially Lithium Iron Phosphate (LiFePO4) batteries are recommended.
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