Mighty Max ML75-12 12V 75Ah AGM Battery

Mighty Max ML75-12 battery is Absorbent Glass Mat (AGM) Sealed Lead-Acid (SLA) deep cycle, maintenance free battery. It features spill-proof design and is intended for wide range of applications including standby and security systems, as wheel chair or trolling motor battery, emergency sump pump battery, electric vehicles battery etc.

Although designed as deep cycle battery, Mighty Max ML75-12 also features relatively high discharge rate, long service life, wide operating temperature, and low self-discharge rate. However, when used in standby applications, smart battery charger/maintainer is highly recommended for keeping the battery fully charged and ready for an emergency.

Published: October 17, 2019.

Mighty Max ML75-12 Features and Specifications

Mighty Max ML75-12 is BCI Group 24 battery, with physical dimensions of (L x W x H) 10.2 x 6.65 x 8.19 inches (26 x 16.9 x 23.1 cm) and weight of 50.71 pounds (~22.97 kg).

Mighty Max ML75-12 is Absorbent Glass Mat (AGM) Sealed Lead-Acid (SLA) battery, requiring practically no maintenance (just keep terminals clean) with no need to check and/or add distilled/demineralized water into its 6 cells.

Although labeled as 75Ah battery, Mighty Max ML75-12 is actually 77Ah battery - when the new, fully charged Mighty Max ML75-12 battery is being discharged at 77°F (25°C) its effective capacity depends on the discharge rate:

- 1 hour rate, 48.5 Amps down to 9.6 volts (1.60 volts per cell): 48.5 Ah effective capacity,

- 5 hour rate, 13.5 Amps down to 10.5 volts (1.75 volts per cell): 67.5 Ah effective capacity,

- 10 hour rate, 7.5 Amps down to 10.8 volts (1.80 volts per cell): 75 Ah effective capacity,

- 20 hour rate, 3.85 Amps down to 10.8 volts (1.80 volts per cell): 77 Ah nominal capacity.

Mighty Max ML75-12 plates are made using calcium-tin-lead alloy, ensuring high power density, and long service life, regardless if the battery is used in standby or cyclic applications.

Self-discharge rate is rather low. New, fully charged battery when stored at 68°F (20°C) retain:

- 90% capacity after being stored for 3 months,

- 80% capacity after being stored for 6 months,

- 60% capacity after being stored for 12 months.

So, when storing Mighty Max ML75-12, store it in cool and dry place and if possible, recharge it when its capacity drops down to 80%. Best case scenario is to store the battery connected to smart AGM battery charger/maintainer that will monitor the battery and keep it fully charged all the time.

Mighty Max ML75-12 features F17 terminal posts, ensuring firm contact.

Mighty Max ML75-12 internal resistance is 8 mΩ, limiting maximum discharge 5 seconds current to ~700 Amps (at 77°F, 25°C) - again, this battery is not intended for starting applications, but if required it can be used occasionally for starting internal combustion engines requiring some 300-350 Amps of current.

When the battery is used in float applications, charging voltage (77°F, 25°C) should be in the 13.6 - 13.8 volts range and for cycling applications, charging voltage (77°F, 25°C) should be in the 14.5 - 14.9 volts range, with maximum current of 18.8 Amps.

Mighty Max ML75-12 AGM Battery Constant Current Discharge Chart

The following chart shows Mighty Max ML75-12 battery constant current discharge rates (at 77°F, 25°C - given in Amps):

End Point Voltage	End Point Voltage (per cell)	5 min	10 min	15 min	30 min	1 hour	3 hours	5 hours	10 hours	20 hours
9.6V	1.60V	237	178	137	82.3	48.5	19.7	14.0	7.88	4.10
9.9V	1.65V	223	168	132	79.8	47.9	19.5	13.9	7.82	4.05
10.2V	1.70V	210	158	126	77.2	46.2	19.2	13.7	7.75	4.00
10.5V	1.75V	196	149	121	74.5	46.5	18.9	13.5	7.65	3.95
10.8V	1.80V	181	140	114	72.0	45.7	18.5	13.2	7.50	3.85

Since it is AGM SLA battery, Mighty Max ML75-12 end voltage differs according to the discharge rate - the longer the discharge time, the higher end voltage must be or the amount of sulphuric acid in the electrolyte will drop too low and the lead sulphate deposits on the battery's plates will rise over safe levels.

Anyway, Mighty Max ML75-12 battery can provide, for example, 237 Amps for 5 minutes, or 7.5 Amps for 10 hours, ensuring proper operation of various systems like UPS devices, wheelchairs, sump pumps and similar.

Mighty Max ML75-12 AGM Battery Constant Power Discharge Chart

The following chart shows Mighty Max ML75-12 battery constant power discharge rates (at 77°F, 25°C - given in Watts):

End Point Voltage	End Point Voltage (per cell)	5 min	10 min	15 min	30 min	45 min	1 hour	2 hours	3 hours	5 hours
9.6V	1.60V	2490	1950	1530	918	720	586.2	329.4	240.0	164.4
9.9V	1.65V	2430	1812	1500	906	702	575.4	323.4	223.2	161.4
10.2V	1.70V	2262	1752	1476	888	690	564.4	317.4	219.0	158.4
10.5V	1.75V	2148	1656	1392	876	672	553.8	311.4	214.8	154.8
10.8V	1.80V	2058	1578	1320	858	654	543.0	306.0	210.6	151.8

Maximum constant output power of Mighty Max ML75-12 battery depends on discharge time and end voltage.

Mighty Max ML75-12 battery can provide, for example, almost 2.5 kW for 5 minutes or 150 watts for 5 hours - important for constant power devices (for example, DC/DC and DC/AC converters and similar).

Mighty Max ML75-12 Cycle Service Life vs. Depth of Discharge (DoD)

However, when the AGM SLA battery is used in cyclic operations and when it is being deeply discharged, its capacity drops after certain number of cycles:

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

- 50% DoD: 80% capacity after ~370 cycles, 60% capacity after ~460 cycles,

- 30% DoD: 80% capacity after ~880 cycles, 60% capacity after ~1200 cycles.

So, if one drains ML75-12 battery regularly down to 50% DoD, one may expect that battery to retain 80% of its nominal capacity (75Ah x 0.80 = 60Ah) after 370 cycles and to retain 60% of its nominal capacity (75Ah x 0.60 = 45 Ah) after 460 cycles.

Note: when the Mighty Max ML75-12 is used in standby applications, one may expect it to retain 80% of its nominal capacity after at least a 6.5 years and to retain at least 60% after 8.7 years.

Mighty Max ML75-12 as a Trolling Motor Battery

Mighty Max ML75-12 is a popular choice as a medium-range trolling motor battery.

Small to medium power trolling motors (up to 50-55 lbs of thrust) feature maximum currents of ~50 Amps.

Mighty Max ML75-12 is able to provide 50 Amps for almost an hour (48.5 Amps for 60 minutes). Since electric trolling motors are rarely used at full throttle all the time during fishing, note that Mighty Max ML75-12 is able to provide 20 Amps for almost 3 hours.

If larger trolling motors are used, larger batteries are required as well, preferably in the 120+ Ah range.

Note: decreasing the motor power greatly increases operating time of the trolling motor on a single battery charge. However, for safety reasons always over-dimension slightly your trolling motor battery.

Mighty Max ML75-12 as a Wheelchair Battery

Wheelchairs commonly use 12 or 24V electric systems. If the wheelchair is using single AGM battery (Mighty Max ML75-12 in this example) and the wheelchair has 2x150W motors, one may expect at least 2h of operation at full throttle (on even terrain).

If the wheelchair comes with 24V system, 2x250W motors and two ML75-12 batteries may fit battery compartment, then one may expect at least 2h and 30 minutes of operation at full throttle (on even terrain).

Since wheelchairs are rarely used at full throttle all the time, actual operating time is usually longer, and depends on many details, which is far beyond this article.

Mighty Max ML75-12 as a Sump Pump Battery

Mighty Max ML75-12 is reliable and affordable battery that is often used to power various system in the emergencies. One of such systems are 12 volts sump pumps.

Sump pumps differ in size, power, static pressure/vertical height, flow, etc.

Sump pumps ranges in power from small pumps usually featuring 1/5 HP to 1 HP or even more.

Note: one horsepower is commonly defined as ~746 W (mechanical, imperial, electrical etc HP) and ~736 W (metric HP).

The following list assumes 1 HP = 746W and lists maximum operating times of sump pumps being powered by new, fully charged ML75-12 battery depending on the sump pump power:

- 1/5 HP: 149.2 watts -> around 5 hours,

- 1/4 HP: 186.5 watts -> slightly more that 3 hours,

- 1/3 HP: 246.6 watts -> 2 and half hours, maybe slightly more,

- 1/2 HP: 373 watts -> slightly less than 2 hours,

- 1 HP: 746 watts -> around 40 minutes.

If you need longer operating time, consider either much larger battery or power generator that kicks in automatically after some time and power required equipment.

How to Charge Mighty Max ML75-12 AGM Battery

Maximum recommended charging current is 18.8 Amps and charging voltage depends on the use:

- Float use: 13.6 - 13.8 volts,

- Cycle use: 14.5 - 14.9 volts.

Although Mighty Max ML75-12 can be recharged quickly using 15-18 Amps smart AGM battery chargers (under 5-6 hours) - such chargers test the battery first, charge it fully using bulk charge phase and then, if required, they may normalize the cells and keep the battery fully charged for longer period of time (trickle charge, battery maintainer mode).

When the battery is used in vehicles, security/medical and other similar systems, battery is charged via battery chargers that came with the vehicle/device itself or one may use dedicated smart AGM battery charger.

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Long Story Short: Mighty Max ML75-12 battery is versatile, general purpose, deep cycle AGM battery that may be mounted in any position, it is resistant to shocks and vibrations, tolerates broad range of temperatures and it comes with 1-year warranty.

It may be used in both cycle and float applications - use it, but don't abuse it and it will serve you well.

For more reviews and recommendations and most up-to-date prices and offers, check Mighty Max ML75-12 12V 75Ah AGM SLA Battery Amazon link (link opens in the new window).