Battery Equivalents and Replacements

How Long Do Marine Batteries Last? Tips and Tricks How To Extend Their Life

Marine batteries range from small lead-acid batteries designed for starting small outboard gasoline engines to large cranking battery banks intended for cranking large diesel engines and large deep-cycle battery banks intended for powering all sorts of loads while the main engine (or engines) are turned off.

As such, marine batteries are one of the most important parts of any boat or yacht, often underappreciated until they show signs of impending failure. Thus, many people wonder how long marine batteries last and how they can extend their lifetime.

Published: February 23, 2023.

ship engine controlls

Quick Intro To Marine Batteries

Marine batteries differ in type, chemistry, size, voltage, capacity, discharge characteristics, etc., just like automotive and industrial batteries.

The two most common marine battery chemistries are lead-acid and lithium chemistries, and they can be divided into:

  • Lead-Acid Wet/Flooded Batteries
  • Lead-Acid Gel Batteries
  • Lead-Acid Absorbent Glass Mat (AGM) Batteries
  • Lithium Iron Phosphate (LiFePO4) Batteries

Other batteries like Nickel Cadmium, Nickel Metal Hydride, Lithium-Ion, Lithium-Polymer, and similar are rarely used.

Also, some boats and yachts use super-capacitors for cranking, but they are also rarely used.

The main differences between these battery types are given in the following comparison chart:

Battery Type Life Expectancy Expected Number of Charging/Discharging Cycles Typical Use
Lead-Acid Wet Cell 2-5 years 200-700 Starting, Deep-Cycle
Lead-Acid Gell 3-6 years 300-800 Mostly Deep-Cycle
Lead-Acid AGM 4-7 years 300-800 Starting, Deep-Cycle
Lithium LiFePO4 6-8 (10) years 2000-5000 Deep-Cycle

Note: some manufacturers offer starting Lithium Iron Phosphate batteries as well, but such batteries are still rare on the market.

Lead-Acid Wet/Flooded Batteries

Lead-acid wet/flooded batteries are the oldest type of marine batteries and are still used as both starting, dual-purpose, and deep-cycle batteries.

They are NOT maintenance-free batteries and must be operated in a vertical position, or dangerous acid can leak out of the batteries.

Due to the toxic fumes, terminal corrosion is quite common. Also, due to the release of flammable hydrogen, they must be operated in a well-ventilated area.

Before jump-starting these batteries, be sure that the area is well-ventilated, or sparks can cause a hydrogen gas explosion. Seriously!

Wet lead-acid deep cycle batteries, on average, tolerate 200-250 charging/discharging cycles down to 100% DoD, 250-300 cycles down to 80% DoD, and 400-600+ cycles down to 50% DoD, but this depends on the battery construction, model, charging temperature, charging current, etc.

marine flooded battery 1

Lead-Acid Gel Batteries

Gel lead-acid batteries are mostly dual-purpose and deep-cycle batteries, but there are also starting gel-cell lead-acid batteries, but they are not that common.

Gel-cell batteries are maintenance-free batteries and feature longer standby life than wet/flooded lead-acid batteries, and support slightly more charging/discharging cycles.

Lead-Acid Absorbent Glass Mat (AGM) Batteries

As their name suggests, Absorbent Glass Mat (AGM) lead-acid batteries feature electrolytes suspended in a glass mat and are maintenance-free batteries, very resistant to vibrations and mechanical shocks.

AGM batteries are used as starting, dual-purpose and deep-cycle batteries. They generally feature a slightly longer standby than Gel-Cell batteries, but this is model dependent.

Also, AGM batteries also support more charging/discharging cycles than Gel-Cell, but this is again very model dependent.

Personally, if You are unsure about your lead-acid battery, go for a proper (starting, dual-purpose, deep-cycle) AGM lead-acid battery and don't look further.

Lithium Iron Phosphate (LiFePO4) Batteries

Lithium Iron Phosphate (LiFePO4) batteries are used almost exclusively as deep-cycle batteries. They must be recharged using lithium battery chargers or charge controllers or the built-in Battery Management Systems (BMS) will protect the batteries by disconnecting them from the rest of the boat's electrical system.

Unlike lead-acid batteries, LiFePO4 batteries support a large number of charging/discharging cycles down to 100% DoD, although even they will last much longer if they are not discharged below 80% DoD.

Also, unlike lead-acid batteries, which MUST be recharged up to 100% in order to break lead-sulfate crystals completely, LiFePO4 batteries prefer charging up to 20% DoD (80% SoC) - charging them to 100% will not "destroy" them in the long run, but may help prolong their lifetime.

Note: Lithium Iron Phosphate batteries don't suffer from capacity loss when discharged with strong currents (up to 1.0C) as lead-acid batteries do, but most of the lithium batteries are not able to provide discharge currents stronger than 1.0C continuously.

small trolling motor

What Kills Marine Battery And How To Avoid It?

There are numerous reasons why marine batteries die, some of them are:

Vibrations and Mechanical Impacts

There is a big difference between having the battery onboard the boat or placed on the floor of some off-the-grid installation.

The amount of vibrations on the boat can be huge - most people don't notice them, but there are all sorts of vibrations, including the main engine vibrations, vibrations due to the waves and wind, vibrations due to the other equipment, etc.

Also, engine rooms on boats and yachts are not very roomy, leading to unintentional impacts in the battery with various wrenches, hammers, screwdrivers, etc.

Solution: place the batteries on rubber or silicon mats/foam and secure them firmly - rubber or silicon mats/foam will dampen the vibrations. Also, be more careful when being around the batteries while in the engine room.

Low and High Temperatures

When the batteries are stored and used at too low or too high temperatures, their operating lifetime is shorter.

Too low temperatures: chemical processes are slower, and batteries must work harder to do the same task.

Too high temperatures: chemical processes are faster, and batteries work less hard, but they also deteriorate faster.

Solution: store and use batteries at room temperature, if possible. If not, during winter, warm-up batteries a little bit, and during summer, try to ventilate the battery compartment with fresh air, or if possible, cool it down with some cold air from the AC unit, if present.

Improper Charging

Marine batteries should be charged using advanced battery chargers combined with temperature probes.

Advanced battery chargers are microprocessor controlled and feature a multi-mode charging process optimized for the exact battery type (wet/flooded, Gel, AGM, Lithium) - after analyzing the batteries, the batteries are charged according to their condition - if the sulfation (lead-acid batteries) is detected, desulfation process is initiated, for example.

After charging, advanced battery chargers enter maintenance mode, keeping the batteries fully charged without overcharging them.

Few notes:

  • Temperature probes are very important, especially when charging lead-acid batteries, which can end up undercharged in winter and overcharged in summer,
  • The charging currents should be around 0.1-0.15C for lead-acid batteries and 0.2-0.3 for lithium batteries. Stronger currents can be used as well but can lead to shorter battery life.
  • Batteries connected to the boat's electrical system should be charged via alternator and charge controller when the engines are turned On or via battery charge controller when the mains power is used in the harbor.

boat charging in harbour

Improper Use

Starting batteries should be used for engine starting/cranking and should NOT be used for deep-discharge applications.

Deep-cycle batteries should NOT be used for engine starting/cranking.

Dual-purpose batteries may be used for both engine starting/cranking and for deep-discharge applications; just one must be aware of their limitations in terms of Cranking Amps (CA/MCA), Cold Cranking Amps (CCA) and supported number of charging/discharging cycles.

When specialized batteries are required, it is recommended to have a dual-battery electrical system, where the cranking battery is connected directly to the engines alternator/charge controller and starter (and its solenoid), and the deep-cycle battery (or battery bank) is connected to the alternator/charge controller via DC-to-DC battery charge controller and the rest of the boats electrical system with all the loads requiring a deep-cycle battery.

Improper Storage

When storing the lead-acid batteries for a longer period of time, do the following:

  • recharge the batteries to 100% DoD,
  • disconnect the battery cables, protecting it from the parasite drain,
  • connect the battery to the battery maintainer (it can be solar powered by a compact solar panel, or one can use a 110/220V AC battery charger/maintainer) that will keep the battery charged while the battery is being stored,
  • store the battery in a cool, dry, well-ventilated area.

After the storage, there is no need to recharge the battery, since the battery is recharged to 100% SoC with cells properly balanced (if the battery charger/maintainer is a good one, so don't go cheap when buying battery charger/maintainer).

If the battery is powering systems that cannot or should not be turned off while the battery is stored, leave the battery cables connected and use 110/220V AC or a solar battery charger/maintainer - in this case, solar battery charger/maintainer should be powered with a somewhat larger solar panel, just in case.

solar panels on boat

When storing Lithium Iron Phosphate (LiFePO4) batteries, charge them to 50-60% SoC and store them in a cool area for up to 5-6 months. Before the first next use, recharge them completely.

Improper Maintenance

Improper maintenance can shorten marine battery life significantly. Typical maintenance tasks include:

  • if You have wet/flooded lead-acid batteries, regularly check the level of electrolyte, and if required, add some distilled water,
  • check the battery terminals and keep them clean, especially if You have lead-acid batteries,
  • monitor the batteries' temperatures and protect them from extra cold and extra hot temperatures,
  • keep the batteries, especially lead-acid batteries, always 100% charged. If You are not in a hurry, keeping the lithium batteries in 50-60% SoC is recommended - recharge them before use.

These are general guidelines for maintaining the battery; however, one also must take into account local conditions and adjust maintenance tasks accordingly.

Frequently Asked Questions (FAQ)

Here are some of the most common Frequently Asked Questions (FAQ) about marine batteries:

How long does a marine battery last?

Depending on the battery chemistry, use, and maintenance, marine batteries may last up to 4-10 years. If You are looking for a lead-acid battery, go for AGM lead-acid battery; if You are looking for a lithium battery, go for deep-cycle Lithium Iron Phosphate (LiFePO4) battery.

What are recommended marine battery brands?

For AGM batteries, go for Odyssey and Optima batteries, and for Lithium batteries, go for Battle Born and/or Dakota Lithium batteries.

For larger lithium battery banks, go for Ampere Time (now LiTime), CHINS, AIMS Power, Lossigy, and similar brands.

battery charging with charger

How often should You charge a marine battery?

If You are using your boat/yacht regularly, especially if the boat/yacht is connected to the shore mains power (110/220V AC) when in the harbor, You should never NEED to charge your marine battery.

However, if You are not going to use your boat for few months and if there is no shore mains power present, either use a battery charger/maintainer with solar panels for lead-acid batteries or recharge them every 2-3 weeks in summer and every 2-3 months in winter.

Lithium batteries should be recharged to 50-60% and stored for 3-6 months.

How often should You change a marine battery?

When the battery/batteries start to show symptoms of weak/dead battery, like slow and lazy starts, dimmed lights, etc., replace your old battery with a new one.

Should You disconnect the boat battery in the winter?

If You don't have any system that MUST stay connected to the battery, it is highly recommended to disconnect the battery in winter.

Few Final Words

A bad battery, either weak or dead, can ruin anybody's fishing or leisure trip, so always keep a good engine battery jump starter ready.

Proper charging and maintaining can prolong the battery's lifetime and save plenty of money, nerves, and effort, so check your battery periodically and act according to its condition.