Battery Equivalents and Replacements

Mighty Max ML8D Deep Cycle AGM Battery

Mighty Max ML8D battery is a large, heavy, BCI Group 8D, deep cycle battery, intended for both standby and cycling use in automotive, marine, and light-industrial applications.

Mighty Max ML8D is a spill-proof, maintenance-free, Absorbent Glass Mat (AGM) Sealed Lead-Acid (SLA) battery that tolerates deep discharges well, is able to provide strong currents, have a low self-discharge rate, and is thus a popular and affordable battery for various uses, including trolling motor battery, UPS battery, off-the-grid battery, medical/security battery, etc.

Published: July 29, 2021.

mighty max ml8d 1

 Mighty Max ML8D Battery Features and Specifications

Mighty Max ML8D battery features physical dimensions of (L x W x H) 20.5 x 10.6 x 8.0 inches (520 x 269 x 203 mm) and it weighs 159 pounds (~72.2 kg).

The battery comes with a pair of carrying handles, allowing two adults to lift it and put it down, but for transporting the battery even to shorter distances, a small trolley or similar carrying aid is highly recommended.

As its label suggests Mighty Max ML8D battery belongs to the BCI Group 8D batteries, which feature maximum battery dimensions of 20.75 x 11.125 x 9.875 inches (527 x 283 x 250 mm) - as one can see, Mighty Max ML8D battery can easily fit any battery compartment intended for the standard BCI 8D batteries.

Mighty Max ML8D battery is a sealed, maintenance-free, and spill-proof battery that can be placed in any position EXCEPT up-side-down.

It is an AGM (Absorbent Glass Mat) battery featuring its electrolyte absorbed by the glass mat - hence the name.

Such design also improves other features of the battery, including a lower self-discharge rate (in combination with improved battery plates), and a higher number of supported deep discharge cycles.

Mighty Max ML8D battery comes with a pair of M8 battery terminals, ensuring a firm connection between the battery and the cables, which must be of required thickness, depending on the anticipated currents.

mighty max ml8d 2

Mighty Max ML8D battery features a nominal voltage of 12V, with charging voltage depending on its use:

- Cyclic Use: 14.5 - 14.9 volts @77°F (25°C) with temperature compensation of -30mV/°C,

- Standby Use: 13.6 - 13.8 volts @77°F (25°C) with temperature compensation of -20mV/°C.

The maximum charging current is 75A.

The capacity of the Mighty Max ML8D battery depends on the discharge rate:

- 100-hour rate, down to 1.8V/cell (10.8V): 269 Ah,

- 24-hour rate, down to 1.8V/cell (10.8V): 250 Ah,

- 10-hour rate, down to 1.75V/cell (10.5V): 245 Ah,

- 5-hour rate, down to 1.75V/cell (10.5V): 201.5 Ah,

- 1-hour rate, down to 1.60V/cell (9.6V): 162.5 Ah.

The maximum allowed discharge current is 1100 Amps with a short circuit current of 4300 Amps - although Mighty Max ML8D battery is a deep cycle battery, thanks to its size, it is able to provide large currents as well.

Personally, Mighty Max ML8D battery and similar batteries can be used as starting batteries for smaller gas and even diesel engines not requiring more than 300-400 Amps for few seconds - batteries like this one should not even notice such load.

mighty max ml8d 3

Self-discharge rate depends on the storage temperature:

- @40°C: ~10-12% per month,

- @30°C: ~5-6% per month,

- @20°C: ~3-3.5% per month.

So, if You plan on storing the Mighty May ML8D battery for a longer period of time, charge it fully and store it in a cold area. If possible, a good AGM battery maintainer may be connected to the battery in order to keep it fully charged during storage.

The number of supported charging and discharging cycles depends on many things, but mostly on the Depth of Discharge percentage (DOD%):

- 10% DoD: ~2500 cycles,

- 20% DoD: ~1600 cycles,

- 50% DoD: ~700 cycles,

- 80% DoD: ~470 cycles,

- 100% DoD: ~300 cycles.

So, in order to prolong the batteries operating life and still have a very useful capacity, keep the DoD% in the 50% to 80% range.

How to Charge the Mighty May ML8D Battery

If the Mighty May ML8D battery is connected to the electric system of the boat, vehicle, or some device that features an alternator with charging electronics suitable for charging the Mighty May ML8D battery, let that alternator with its charging electronics do the job.

However, if the Mighty May ML8D battery is charged directly, one should have a strong AGM smart battery charger, solar charge controller, or similar device.

With the 75 Amps maximum charging current, battery chargers in the 25-50 Amps range are highly recommended. Some of those chargers are (Amazon links, open in the new windows):

- NOCO Genius Pro25 with the maximum charging current of 12V batteries of 25 Amps,

- NOCO Genius Pro50 with the maximum charging current of 12V batteries of 50 Amps.


Of course, both units support charging batteries of various voltages (6V, 12V, 24V), chemistries (lead-acid, lithium), types (AGM, Gel-Cell, etc.), but also come with other features as well, like being able to act as power supplies and similar.

These units are not cheap, but nor are the batteries they are intended to charge!

Of course, there are other similar battery chargers on the market, so choose according to your own needs and preferences.

Long Story Short: Mighty Max ML8D battery is a large and heavy, high-capacity BCI Group 8D battery, being able to store and deliver a large amount of energy.

Although it is a deep cycle battery, it is able to provide large currents too.

But, that is not what this battery is designed for - it is an excellent battery for standby and cycling applications where currents are kept relatively low (preferably under 0.5-1.0C) and where the battery is not regularly discharged below 80%.

So, if You are looking for such a BCI 8D battery, consider Mighty Max ML8D.

For more reviews and recommendations, feel free to follow the Mighty Max ML8D Deep Cycle AGM Battery Amazon link (link opens in the new window).