Optima 34M BlueTop Marine Starting Battery

Optima 34M BlueTop Marine Starting Battery is very popular SLA AGM marine battery commonly used as the starting/cranking battery in smaller fishing boats. Although it can be used as dual purpose, or even as deep cycle battery (not recommended, of course), it is best used in applications, which it was designed for - as reliable, relatively lightweight, but strong cranking battery.

optima 34m bluetop 1

Optima 34M BlueTop differs from other Optima D27M, D31M and D34M batteries is that is designed for marine starting applications - it is able to provide large currents for starting internal combustion engines, but it doesn't tolerate well deep discharges.

Although it can be used as dual purpose and even as deep cycle battery, such use shorten operating time of the battery. Personally, don't discharge starting battery regularly below 50% of its capacity.

Following table compares Optima 34M BlueTop starting battery with other Optima BlueTop batteries.

Model Battery Type Goup Size Cell Type Ah CCA MCA RC Weight (lbs/kg)
Optima 8027-127 D27M Dual Purpose 27 AGM 66 800 1000 140 54 lbs; 24.5 kg
Optima 8052-161 D31M Dual Purpose 31 AGM 75 900 1125 155 61 lbs; 27.6 kg
Optima 8016-103 D34M Dual Purpose 34 AGM 55 750 870 120 46 lbs; 21 kg
Optima 8006-006 34M Starting/Cranking 34 AGM 50 800 1000 100 38.4 lbs; 17.4 kg

Note: Amazon links open in the new windows, feel free to check them.

optima d34m d27m d31m 1m

As one can see Optima 34M is the lightest of these 4 SLA AGM marine batteries.

For example, main difference between 34M and D34M is that D34M is designed as dual purpose battery, thus, it has thicker lead plates and can withstand more deep charge/discharge cycles, but its cranking power is not as good as cranking power of Optima 34M battery.

Battery weight: Optima 34M is the lightest - 34M weighs 38.4 lbs, D34M weighs 46 pounds, D27M weighs 54 pounds and D31M weighs 61 pounds.

Their relative cranking power is ratio between MCA/CCA and their weight and these batteries are able to provide:

optima d31m bluetop- 34M: 26 MCA Amps per 1 pound of weight,
- D34M: 18.9 MCA Amps/pound,
- D27M: 18.5 MCA Amps/pound
- D31M: 18.4 MCA Amps/pound.

Obvious starting battery winner is Optima 34M BlueTop battery.

Relative RC is usually given in the minutes per pound and for these four batteries it is:

- 34M: 2.6 minutes/pound,
- D34M: 2.6 minutes/pound,
- D27M: 2.59 minutes/pound,
- D31M: 2.54 minutes/pound.

It would be false to conclude that Optima 34M is good deep cycle battery just by its RC value. Problem is that this battery is not designed for deep cycle use and such frequent discharges can quickly ruin the battery - even up to 4x faster than dual purpose/deep cycle battery.

Optima 34M BlueTop Marine Starting Battery Recommended Use

optima bluetop darkgray starting batteryOptima 34M BlueTop should be used as the starting battery only.

For boats and smaller yachts with dual battery system, Optima 34M BlueTop should be used as the starting/cranking battery and its charge should be maintained with alternator found on the main boat engine(s) - just like in the car.

Designated dual purpose or preferably deep cycle marine battery should be used as second battery and used for all other purposes like lights, electronics and other appliances. This second battery can be charged using alternator(s) on main boat engine(s), but also via dedicated power generator, wind turbine and/or solar panels.

For boats with single battery system, Optima 34M BlueTop should be used as starting battery and for powering few small electric loads like LED lights, smaller electronic devices, for charging smartphones and tablets and similar.

In this configuration, battery should be charged using alternator(s) from main boat engine(s). However, should you plan not to use main engine regularly, smaller solar panels connected to the battery via solar charger(s) can help avoid deep discharges of the battery.

For boats with single battery system, but with plenty of electronics and electric devices, Optima 34M BlueTop should not be preferred choice - it can be used, but it will not last a long time and can have issues with starting the boat engines when being discharged.

Also, keep in mind that larger dual purpose batteries can provide more than enough cranking Amps, even after powering lighter load for hours. And yes, such batteries are heavier and more expansive, but nobody wants a dead battery miles and miles away from land or nearest port.


Long Story Short: Optima 34M BlueTop is good and popular starting marine battery. It is not designed for cyclic use and such use should be avoided.

It is of AGM design and thus, spill proof.

For more reviews and recommendations, check Optima 34M BlueTop Marine Starting Battery Amazon link (link opens in the new window).