Mighty Max ML18-12 AGM Deep Cycle Battery

Mighty Max ML18-12 battery is a Sealed-Lead Acid (SLA) Absorbent Glass Mat (AGM) general purpose battery, intended for standby/float and deep cycle applications. Mighty Max Battery ML18-12 battery is a spill-proof and vibration-resistant battery that can operate in almost any position (up-side-down not recommended) and is almost maintenance-free.

Mighty Max Battery ML18-12 is a reliable battery that comes at an affordable price and is thus one of the most popular batteries in its class, often used as wheelchair battery, generator battery, UPS battery, as standby battery in medical and security systems, as fish finder battery, small trolling battery, etc.

Published: June 1, 2020.

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Mighty Max ML18-12 Features and Specifications

Mighty Max ML18-12 battery is compact and relatively lightweight AGM battery featuring physical dimensions of (L x W x H) 7.13 x 3.03 x 6.57 inches (~181 x 77 x 167 mm). Also, it weighs 11.2 pounds (~5.1 kg).

Mighty Max ML18-12 is general purpose battery, but it is often used as standby and deep cycle battery - it may be used as starting battery for small power generators, lawnmowers, and similar units that come with a small internal combustion engine, however, for such use small starting motorcycle/Powersports battery is a better choice.

Nominal capacity of the Mighty Max ML18-12 is 18 Ah - capacity when the battery is being discharged for 20h down to 10.5 volts. Like all SLA AGM batteries, Mighty Max ML18-12 is experiencing capacity loss as the discharge current is being increased:

- 20h rate: 18Ah capacity - 0.90 Amps down to 10.5 volts,

- 10h rate: 16.2Ah capacity - 1.62 Amps down to 10.5 volts,

- 5h rate: 14.5Ah capacity - 2.9 Amps down to 10.5 volts,

- 1h rate: 11Ah capacity - 11 Amps down to 9.6 volts,

- 30 min rate: 9.6 Ah capacity - 19.2 Amps down to 9.6 volts.

Although such capacity drop (50% for 30 minutes discharge) appears large (and it is!), it is a typical capacity loss for general-purpose SLA AGM batteries.

When the Mighty Max ML18-12 battery is fully charged, its internal resistance is 16 Ωm (at 77°F, 25%C), ensuring that the battery may provide 255 Amps for 5 seconds (also at 77°F, 25°C).

Mighty Max ML18-12 battery features a relatively low self-discharge rate. When the battery is stored at 68°F (20°C), a capacity loss is ~3% per month:

- remaining capacity after 3 months: 90%,

- remaining capacity after 6 months: 80%,

- remaining capacity after 12 months: 60%.

Note: these are values for the new battery, initially fully charged. When storing lead-acid batteries, low temperatures are preferred. However, connecting the fully charged battery to the battery maintainer can prolong storage time significantly.

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Mighty Max ML18-12 battery feature F3 terminals, with the positive terminal post on the right side of the battery.

When the battery is being used in standby/float applications, the recommended charging voltage is 13.6 - 13.8 volts (77°F, 25°C) and for cycling applications, the recommended charging voltage is 14.5 - 14.9 volts.

The maximum recommended charging current is 5.4 Amps - when the battery is discharged down to 50% DoD, a smart AGM battery charger with 4 Amps maximum charging current can fully charge the battery in ~2.5 hours.

When the battery is being used in deep cycle operations, its operating life is defined as the number of charging/discharging cycles that the battery may withstand with the certain capacity loss:

- 100% DoD: ~180 charging/discharging cycles with the capacity loss down to 80% of nominal capacity, ~200 cycles charging/discharging cycles with the capacity loss down to 60% of nominal capacity,

- 50% DoD: ~360 charging/discharging cycles with the capacity loss down to 80% of nominal capacity, ~400 cycles charging/discharging cycles with the capacity loss down to 60% of nominal capacity,

- 30% DoD: ~850 charging/discharging cycles with the capacity loss down to 80% of nominal capacity, ~1150 cycles charging/discharging cycles with the capacity loss down to 60% of nominal capacity.

If the battery is used often, it is a good practice not to discharge it completely. On the other hand, if the battery is being discharged only from time to time, discharging it even down to 100% DoD will not harm the battery.

Also, don't let the lead-acid battery remain discharged for a longer period of time - if there is no need to let the battery cool down, recharge it immediately.

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Mighty Max ML18-12 Battery Discharge Charts

Constant current discharge features for the Mighty Max ML18-12 battery are given in the following chart - values are given in Amps, measured at 77°F/25°C:

Cell End Voltage Battery End Voltage 5 min 10 min 15 min 30 min 1 hour 3 hours 5 hours 10 hours 20 hours
1.60 volts 9.6 volts 63.7 42.8 32.6 19.2 11.0 4.49 3.05 1.68 0.89
1.65 volts 9.9 volts 61.4 41.8 31.8 18.8 10.7 4.40 3.00 1.66 0.88
1.70 volts 10.2 volts 59.1 40.8 31.0 18.4 10.4 4.30 2.95 1.64 0.87
1.75 volts 10.5 volts 56.8 39.6 30.2 18.0 10.0 4.21 2.90 1.62 0.85
1.80 volts 10.8 volts 54.5 38.6 29.4 17.5 9.7 4.12 2.85 1.60 0.84

Constant power discharge features for the Mighty Max ML18-12 battery are given in the following chart - values are given in watts, measured at 77°F/25°C:

Cell End Voltage Battery End Voltage 5 min 10 min 15 min 30 min 45 min 1 hour 2 hours 3 hours 5 hours
1.60 volts 9.6 volts 774 490 389 228 167 134 87 63 41.3
1.65 volts 9.9 volts 750 475 380 221 161 129 81.6 59 39.4
1.70 volts 10.2 volts 720 456 365 214 154 122 76.8 54.5 37.4
1.75 volts 10.5 volts 678 436 350 206 147 116 72 49.7 35.3
1.80 volts 10.8 volts 642 415 336 197 139 108 65.4 44.3 32.8

 As one can see, Mighty Max ML18-12 is strong enough to provide ~30 Amps or 350 Watts for 30 minutes, without being drained too low.

Mighty Max ML18-12 may provide even more power for shorter periods of time if required, but such discharge conditions lower the actual capacity of the Mighty Max ML18-12 (or any other similar AGM battery) down to ~5 Ah - and that is just ~28% of nominal 20h capacity.

Because of that, Mighty Max ML18-12 and similar batteries are used as wheelchair batteries (often in pairs), scooter batteries, lawnmower batteries, UPS batteries, etc.

Mighty Max ML18-12 as the Wheelchair Battery

Mighty Max ML18-12 is often used in pairs to provide power to wheelchairs. Two Mighty Max ML18-12 are able to power 2x200W motors up to 30 minutes, constantly, after which they must be recharged fully.

Since wheelchairs are not used at full power all the time, the operating time of these batteries in wheelchairs is usually much longer.

Mighty Max ML18-12 as the Fish Finder and Trolling Motor Battery

Mighty Max ML18-12 is commonly used on kayaks, rafts, pontoons, inflatables, and other small vessels as a general-purpose battery.

When being used to power fish finder and other similar devices, the operating time of Mighty Max ML18-12 depends on the current draw of such a device.

garmin striker 4For example, Garmin Striker 4 Fish Finder (Amazon link, links opens in the new window, photo on the right) is one of the most popular compact fish finders, requires around 0.23 - 0.25 Amps of current.

Mighty Max ML18-12 is large enough to power such fish finder for three days in the row (more than 72 hours!).

However, if the larger units are used - the units with larger screens, stronger transducers, and similar - current draw can increase to 2-3 Amps. Such devices may be powered by Mighty Max ML18-12 for up to 5-7 hours.

As the trolling motor battery, Mighty Max ML18-12 is large enough to provide power for short trips only (lasting few minutes).

Small kayak electric trolling motors feature maximum discharge currents in the 25-40 Amps range and the Mighty Max ML18-12 is able to power such units for 10-20 minutes, with almost no safety reserve.

But, when the motor is throttled down to, for example, 15 Amps, Mighty Max ML18-12 is able to power such unit up to 30 minutes with some safety reserve.

Since most people prefer to paddle when using kayaks, trolling motors are often used only for short hops (1-2 minutes), often just to quickly change fishing location, or to get to the nearest shore in an emergency - for such short power burst (up to 40 Amps), Mighty Max ML18-12 is well suited.

However, if you need a lightweight battery being able to store much more energy, consider lithium trolling batteries - they are lighter, energy more efficient, but they also cost more.


migthy max ml18 12 w200pxLong Story Short: Mighty Max ML18-12 is a very popular 12V 18Ah general purpose battery - it is a reliable, rather compact, and durable battery that comes at an excellent price.

It is one of the most popular batteries in its class for a longer period of time, tested by countless users in many real-life situations.

For more reviews and recommendations, feel free to check Mighty Max ML18-12 AGM Battery Amazon link (link opens in the new window).