Battery Equivalents and Replacements

Mighty Max ML55-12 12V 55Ah AGM Deep Cycle Battery

Mighty Max ML55-12 AGM battery is 12V 55Ah general purpose, deep cycle AGM (Absorbent Glass Mat) SLA (Sealed Lead Acid) battery. It features high vibration resistance and spill proof design, allowing it to be used virtually in any position.

Mighty Max ML55-12 AGM battery is commonly used as mid-size trolling motor battery, fish finder battery, for off-the-grid applications, backup and security systems, etc.

Updated: October 16, 2019.

mighty max ml55 12 1

Mighty Max ML55-12 Battery Features and Specifications

Mighty Max ML55-12 is made out of tough ABS plastic, using calcium-tin alloy plates, with fiberglass mat separator and sulfuric acid as electrolyte.

Its physical dimensions are (L x W x H) 9.02 x 5.43 x 8.19 (9.13 including terminals) inches (22.91 x 13.79 x 20.79/23.19 cm).

Physically, Mighty Max ML55-12 is very close to the 22NF BCI Battery Group (9 7/16, 5 1/2, 8 15/16 inches), except that its is slightly taller with the terminals (9.13 vs 8.94 inches) - have this in mind when ordering this battery.

Mighty Max ML55-12 weight of 36.96 pounds (16.74 kg) makes it relatively light for 55-58 Ah battery.

Mighty Max ML55-12 should be charged as soon as it is discharged using smart AGM battery chargers.

When the battery is used in standby (float) applications, its maximum charging voltage should be 13.6-13.8 volts at 77°F (25°C).

When the battery is used for cyclic applications, its end voltage should be in the 14.4-14.7 volts range.

In any case, maximum charging current should not exceed 16.5 Amps.

Mighty Max ML55-12 comes with nuts and bolt (NB) type of terminal posts (F5).

mighty max ml55 12 terminal

Also, to help it carry around, Mighty Max ML55-12 features built-in handles - since it weighs ~37 pounds (<17 kg) it can be more or less easily carried around by an adult, which is very important when setting/placing the battery in the boat, kayak, pontoon, UPS device, and similar.

Nominal voltage of the Mighty Max ML55-12 battery is 12V and nominal capacity is 55 Ah. However, when the battery is discharged for 20h down to 10.8 volts, on average Mighty Max ML55-12 features 58Ah capacity.

As the discharge current is increased, capacity decreases, which is common for all lead acid batteries:

Battery Capacity

@77°F (25°C)

20h rate (2.9 Amps, down to 10.8V) 58 Ah
10h rate (5.5 Amps, down to 10.8V) 55 Ah
5h rate (9.6 Amps, down to 10.5V) 48 Ah
1h rate (35.2 Amps, down to 9.6V) 35.2 Ah

Note: As the battery is being discharged faster, due to the fiberglass separator, end output voltage (when the battery is considered as being discharged) is lower - 10.5 volts for 5h rate and 9.6 volts for 1h rate.

After discharging battery for, for example, 1h down to 9.6 volts, battery voltage may increase slightly even without charging due to the natural electrolyte mixing - don't discharge such battery any more. Actually, charge it as soon as possible.

Times of flooded cells with builtin pumps for mixing electrolyte are long gone, at least for applications where Mighty Max ML55-12 is going to be used! Yes, author of this article is that old :)

Mighty Max ML55-12 battery features 8 mΩ internal resistance and although it is intended for deep cycle operations, it is able to provide 550 Amps for 5 seconds at 77°F (25°C).

Also, when being discharged for 5 minutes down to 1.6 volts per cell (9.6 volts per battery), new, fully charged Mighty Max ML55-12 is able to provide 172 Amps.

For short, Mighty Max ML55-12 is not intended for starting applications, but if you have internal combustion engine with starter that draws less than 170 Amps, feel free to start it with Mighty Max ML55-12 AGM battery.

If the starter motor requires anywhere between 170 and 550 Amps, don't crank it for more than 5 seconds.

Personally, I would NOT use this battery as a starter battery for motor starters that require more than 150-200 Amps. Mighty Max ML55-12 is not intended for such use and after all, there are smaller and cheaper starter batteries with better cranking performances available on the market.

mighty max ml55 12 2

 Mighty Max ML55-12 battery features low self discharge rate. When the battery is stored at 68°F (20°C), its self discharge rate is:

- 90% after 3 months,

- 80% after 6 months,

- 60% after 12 months.

Higher storage temperatures increase the self discharge rate and lower temperatures decrease the self discharge rate - regardless of the storage temperatures, it is recommended to charge the battery when the capacity drops down to 80% or, preferably, to store the battery connected with the smart AGM battery maintainer which continuously monitors the battery condition and act accordingly.

Maximum number of charging/discharging cycles depends on the Depth of the Discharge (DoD) and is determined with the nominal capacity loss:

- 100% DoD: 80% capacity after ~180 cycles, 60% capacity after ~220 cycles,

- 50% DoD: 80% capacity after ~350 cycles, 60% capacity after ~460 cycles,

- 30% DoD: 80% capacity after ~850 cycles, 60% capacity after ~1150 cycles.

So, in order to prolong its operating life, don't fully discharge Mighty Max ML55-12 (or any other) AGM battery.

Since Mighty Max ML55-12 comes with 1 year warranty, if you drain it daily down to 50% of DoD, it will operate properly during its warranty period.

However, if you use it as trolling motor battery during summer (80-90 charging/discharging cycles) and store it properly during winter, one can expect this battery to last two years.

Note: personally, I never use any battery when its nominal capacity drops below 80% - recycle it properly and get a new one.

Mighty Max ML55-12 AGM Battery Constant Current Discharge Chart

The following chart shows Mighty Max ML55-12 battery constant current discharge rates (at 77°F, 25°C):

Cell End Point Voltage Battery End Point Voltage 5 min 10 min 15 min 30 min 1h 3h 5h 10h 20h
1.60 V 9.6 V 172 130 98.0 58.2 35.2 14.5 9.98 5.69 2.98
1.65 V 9.9 V 162 123 94.0 56.5 34.4 14.3 9.88 5.65 2.97
1.70 V 10.2 V 152 115 89.5 54.5 33.6 14.0 9.75 5.60 2.95
1.75 V 10.5 V 141 108 84.4 52.9 32.7 13.7 9.60 5.55 2.93
1.80 V 10.8 V 128 100 80.5 51.0 31.6 13.4 9.43 5.50 2.90

As one can see, Mighty Max ML55-12 is able to provide ~35 Amps for an hour, which is more than enough for most smaller trolling motors or even smaller electric vehicles. With 2.90 Amps current for 20h, Mighty Max ML55-12 can power even large fish finder GPS combos for 20+ hours.

Note: just be sure to monitor end voltages as they depend on the discharge rate - check discharge graphs that come with the battery and always leave yourself a safety margin when doing calculations.

Mighty Max ML55-12 AGM Battery Constant Power Discharge Chart

The following chart shows Mighty Max ML55-12 battery constant power discharge rates (at 77°F, 25°C):

Cell End Point Voltage Battery End Point Voltage 5 min 10 min 15 min 30 min 45 min 1h 2h 3h 5h
1.60 V 9.6 V 1920 1482 1146 690 530.4 428.4 255.0 182.4 116.4
1.65 V 9.9 V 1860 1398 1098 678 348.4 418.8 250.2 177.0 114.6
1.70 V  10.2 V 1746 1320 1056 666 511.8 409.2 244.8  173.4 112.8
1.75 V  10.5 V 1626 1242 1008 654 500.4 399.6 238.8 169.8 112.2
1.80 V  10.8 V 1542 1152 954 642 487.2 389.4 232.8 166.2 111.0

When being used for high drain applications, Mighty Max ML55-12 battery can provide almost 2kW for 5 minutes and almost 700W for 30 minutes.

Again, monitor end voltages (battery fully discharged) during high drain operations.

When there is no need to push the battery to its limit, keep the end voltages above 10.8 volts regardless of the current drain - although this will decrease available energy that the battery can provide, it will prolong its operating life.

Of course, for standby applications, when the battery is not going to be drained often, draining it down to 100% of DoD is more than justified - battery capacity will deteriorate due to its age and not the charging/discharging cycles.

Mighty Max ML55-12 as Trolling AGM Battery

mighty max ml55 12 mMighty Max ML55-12 is commonly used on small boats, pontoon and kayaks as general purpose battery.

Although it can be used for starting small marine outboard motors, for powering navigation lights, various electric and electronic devices, most commonly it is used as the trolling motor battery.

Due to its size, weight and features, it can be used for powering smaller trolling motors in the 30-40 pounds range. Such electric motors draw up to 40 Amps when used at maximum power.

Decreasing the output power also decreases current draw, prolongs the operating time on the single charge.

Some of the most popular smaller trolling motors are Minn Kota Endura C2 and Newport Vessels NV-Series electric trolling motors.

Minn Kota Endura C2 vs Newport Vessels NV-Series Trolling Motors

Minn Kota Endura C2 series of trolling motors feature thrusts in the 30-55 lbs range and Newport Vessels NV-Series of trolling motors feature thrusts in the 36-86 lbs range.

Their smaller models are often used on various boats, pontoons, rafts, kayaks, inflatables etc and they usually draw currents in the 30-40 Amps range.

Model Minn Kota Endura C2 30 Minn Kota Endura C2 40 Newport Vessels NV-Series 36lb Newport Vessels NV-Series 46lb
Photo minn kota endura c2 30 minn kota endura c2 40 nw 36 lbs nw 46 lbs
Maximum Thrust 30 pounds (~13.6 kg) 40 pounds (~18.1 kg) 36 pounds (~16.3 kg) 46 pounds (~20.9 kg)
 Maximum Current 30 Amps 42 Amps 30 Amps 40 Amps
Recommended Circuit Breaker 50 Amps 50 Amps 40 Amps 50 Amps
Voltage 12V 12V 12V 12V
Speeds 5 Fw, 3 Rv 5 Fw, 3 Rv 5 Fw, 3 Rv  5 Fw, 3 Rv 
Amazon Link Minn Kota Endura C2 30 Minn Kota Endura C2 40 Newport Vessels NV-Series 36lb Newport Vessels NV-Series 46lb

Note: Amazon links open in the new window, feel free to check them for most up-to-date offers and prices.

Both Minn Kota Endura C2 30 and Newport Vessels NV-Series 36lb feature 30 Amps max current and they can be powered using new, fully charged Mighty Max ML55-12 battery for at least an hour, without the battery voltage dropping below 10.8 volts. If the power is decreased, for example, down to 15 Amps, Mighty Max ML55-12 can power these motors for more than 2 hours with good safety margin.

Larger motors that draw ~40 Amps at full throttle, can be powered for at least 30 minutes, without the voltage dropping below 10.8 volts and with good safety margin.

Larger electric trolling motors that draw 50+ Amps also can be powered with Mighty Max ML55-12 battery, however, such strong currents tend to discharge the battery rather quickly - for such applications, larger trolling motor battery is recommended.

For short, if you need good kayak trolling motor battery, consider Mighty Max ML55-12 AGM battery (Amazon link, opens in the new window).

Mighty Max ML55-12 AGM Battery as the Fishfinder Battery

garmin striker 4Mighty Max ML55-12 battery is often used to power fishfinders and other similar marine electronics (radios, GPS units, chart-plotters etc.).

How long Mighty Max ML55-12 can power such units depends on the current draw.

For example, one of the most popular fishfinders is Garmin Striker 4 (Amazon link, opens in the new window), which is very often used on boats, kayaks and pontoons.

When being powered with 12V battery, Garmin Striker 4 draws 0.23 Amps (230 mA) and during a single fishing day (12h for example), it discharges slightly less than 3Ah from the battery.

With its 20 hour capacity of 58Ah, 3Ah discharge during 12h of fishing is almost nothing for Mighty Max ML55-12 and similar batteries.

Larger fishfinder, GPS, chart-plotter combo units draw usually up to 2.5-3 Amps and during 12h fishing period, they can discharge some ~36 Ah from 58 Ah battery.

Such discharge puts Mighty Max ML55-12 down to 62% DoD (38% SoC) and personally, if you want your battery to last for a long time, charge it.

If required, with some 20-22Ah remaining in the Mighty Max ML55-12 battery, if required, it is able to power smaller trolling motor for perhaps 30 minutes, but this puts battery very close to the 100% DoD (0% SoC).

Regardless if you need to power just one small fishfinder, or several similar devices, Mighty Max ML55-12 is suitable for such task and can deliver required power for hours to come - just do the math and check actual Amps that are drawn from the battery. Better safe than sorry :)

How to Charge Mighty Max ML55-12 AGM Battery

optima digital 1200Depending the use, Mighty Max ML55-12 end-voltage should be:

- float (standby) use: 13.6-13.8 volts,

- cycle use: 14.4 - 14.7 volts,

with the maximum charging current of 16.5 Amps. Note: these values are given for the charging temperature of 77°F (25°C).

Smart, microprocessor controlled AGM battery chargers with the currents between 6-12 Amps are highly recommended.

Before actual charging, such chargers test the battery to determine its condition, Depth of Discharge (DoD), charging temperature and other parameters and only then start the charging process. When the battery is fully charged, they go into the so-called maintenance mode where they monitor battery and keep it fully charged (trickle charge).

Battery chargers that can recover deeply discharged AGM batteries and that can normalize cells are highly recommended, especially when there are more batteries to charge and maintain.

Some of the most popular AGM battery chargers that meet such requirements are:

- Optima Digital 1200 12V Performance Battery Charger and Maintainer

- BatteryMinder 128CEC1: 12V 2/4/8 AMP Battery Charger-Maintainer-Desulfator

- NOCO Genius GEN1 10 Amp 1-Bank On-Board Battery Charger

- VMAX BC12M248 12 Volt 8 Amp 7-Stage Smart Battery Charger Maintainer

But, there are other good AGM battery chargers on the market as well.

noco gen 1Personally - although 16.5 Amps is stated as the Mighty Max ML55-12 maximum charging current, I would limit the charging current to 12-13 Amps, especially during warmer (68°F, 20°C or more) months.

When the Mighty Max ML55-12 is (almost) fully discharged, it takes some 6-7 hours to charge it using 10-12 Amps battery charger and up to 12-15 hours to charge it using 5-6 Amps battery charger.

So, keeping the charging current around 10-12 Amps, battery is charged relatively quickly, but it is also not pushed to its limit and extra warming of the battery cells is avoided - assuming that the charging temperature is 68-77°F (20-25°C) and that there is at least some ventilation around the charger and the battery.

Mighty Max ML55-12 vs Optima D34M BlueTop vs VMAXTANKS MR96-60

Mighty Max ML55-12, Optima D34M BlueTop and VMAXTANKS MR96-60 are AGM batteries of similar capacity. Their most important features and specifications are given in the following chart:

Battery Mighty Max ML55-12 Optima D34M BlueTop VMAXTANKS MR96-60
Photo mighty max ml55 12 m  optima d34m table  vmax mr96 60 table 
BCI Group Size ~22NF 34 22NF
Capacity 55 Ah (58 Ah) 55 Ah 60 Ah
MCA (550 Amps for 5 sec) 870 Amps 600 Amps
Reserve Capacity (RC) 35.2 Amps for 1h (down to 9.6V)
14.0 Amps for 3h (down to 10.2V)
120 min 120 min
Weight 36.96 lbs (16.74 kg)  43.5 lbs (19.7 kg) 43 lbs (19.5 kg)
Warranty 1 Year 2 Years 1 Year
Terminal Posts Nuts & Bolts (F5) Dual SAE and 5/16" Stainless Steel Studs 6mm Bolts
Built-In Handles Yes No Yes
Internal Resistance ~8mΩ ~2.8mΩ ?
Amazon Link Mighty Max ML55-12 Optima D34M BlueTop VMAXTANKS MR96-60

Note: Amazon links open in the new window, feel free to check them for most up-to-date offers and prices.

Mighty Max ML55-12, Optima D34M BlueTop and VMAXTANKS MR96-60 are very similar in terms of 20h capacity (55Ah (58Ah), 55Ah, 60Ah respectively), but there are also few very important differences:

- Mighty Max ML55-12 is intended for deep cycle applications. Although it is able to provide 550 Amps for 5 seconds, it should not be used as cranking battery, except perhaps for smaller engines with 100-150 Amps starters.

But, it is lighter than other batteries by ~6 lbs (~2.5 kg) and it is rather affordable.

- Optima D34M BlueTop is designed as true dual purpose marine battery, featuring excellent 750 CCA (Cold Cranking Amps), 870 MCA (Marine Cranking Amps), 120 minutes RC and dual SAE and 5/16" Stainless Stud terminals.

Optima D34M BlueTop is also the heaviest of these three batteries. But, it also comes with 24 months warranty.

- VMAXTANKS MR96-60 is dual purpose battery with the performances between Mighty Max ML55-12 (deep cycle) and Optima D34M BlueTop (dual purpose, excellent starting features) AGM batteries. As starting battery, it is weaker than Optima D34M (600 vs 870 MCA), but it is also better suited for such applications than Mighty Max ML55-12. When being drained for 20h, VMAXTANKS MR96-60 features the best capacity.

But, VMAXTANKS MR96-60 is also heavier than ML55-12 by some 6 pounds and just slightly lighter than Optima D34M battery.

Long Story Short: Mighty Max ML55-12 AGM battery is well balanced and affordable, general purpose deep cycle AGM battery.

It can be used for applications requiring both low to medium currents and for standby applications. It is vibration resistant battery that can be operated in any position.

Also, it is relatively lightweight.

If you are looking for 50-60Ah equivalent AGM, deep cycle battery, consider this model.

For more reviews and recommendations, check Mighty Max ML55-12 AGM Battery Amazon link (link opens in the new window).