When shopping for marine batteries, West Marine customers are often surprised by the tremendous variation in price between the batteries we sell. This variation in price aligns with the different battery chemistries that we offer, which are flooded batteries, and sealed batteries whose chemistries include AGM, gel and lithium iron phosphate. Note: Throughout this discussion, we refer to lithium iron phosphate batteries as “lithium” for short.
Much of the “sticker shock” stems from the price of lithium batteries which can easily cost over one thousand dollars. In a recent West Advisor article Are Lithium Batteries a Good Choice for You? we discuss how the high price of lithium batteries is offset over time by their superior performance compared to flooded, AGM and gel. But given the superior performance of lithium batteries, are they necessarily the best choice for you? The answer is that for many boaters, the best battery for their boat will be one that delivers the energy their boat needs at a price they can afford.
High cranking power for quick engine start
Starting your Engine: Very good
Powering Electronics: Poor
Extending your day on the water: Poor
Starting your engine, powering electronics and accessories
Starting your Engine: Good
Powering Electronics: Fair
Extending your day on the water: Fair
Long lasting power for trolling motors, electronics and accessories
Starting your Engine: Fair
Powering Electronics: Good
Extending your day on the water: Very good
Superior durable technology for starting, trolling motors, and powering electronics and accessories
Starting your Engine: Very good
Powering Electronics: Very good
Extending your day on the water: Very good
Longest lasting, all-in-one solution for powering all your onboard systems
Starting your Engine: Very good*
Powering Electronics: Very good
Extending your day on the water: Very good
High cranking power for quick engine start
Starting your Engine: Very good
Powering Electronics: Poor
Extending your day on the water: Poor
Starting your engine, powering electronics and accessories
Starting your Engine: Good
Powering Electronics: Fair
Extending your day on the water: Fair
Long lasting power for trolling motors, electronics and accessories
Starting your Engine: Fair
Powering Electronics: Good
Extending your day on the water: Very good
Superior durable technology for starting, trolling motors, and powering electronics and accessories
Starting your Engine: Very good
Powering Electronics: Very good
Extending your day on the water: Very good
Longest lasting, all-in-one solution for powering all your onboard systems
Starting your Engine: Very good*
Powering Electronics: Very good
Extending your day on the water: Very good
*Applies to select models only.
Battery Types: Starting, Deep Cycle and Dual Purpose
West Marine offers three different types of batteries: Starting, deep cycle and dual-purpose. When choosing a battery, first consider how the battery will be used. For example, will it be used for starting an engine, powering “house” loads or maybe for both? When considering what type (or types) of batteries you need, it is important to take into account the best use for each type of battery chemistry. Flooded batteries are offered in variations for starting, deep cycle and dual-purpose use. The AGM batteries we offer are all designed for dual-purpose use. The gel batteries we offer are all designed for deep cycle use. The lithium batteries we offer are nearly all for deep cycle use, the exception being Relion's HP line of dual-purpose batteries like their RB100-HP Lithium Dual Purpose Battery, which is suitable for engine starting or deep cycle applications. For an expanded discussion of starting, deep cycle and dual- purpose batteries, see our West Advisor article How to Select a Marine Battery.
Dual-purpose batteries are designed for deep cycle and engine starting applications.
Create an energy budget.
In addition to choosing the right type of battery, the battery (or batteries) you select must have the capacity (rated in amp-hours and reserve minutes) you need to meet your boat’s energy needs. Deep cycle batteries must have adequate capacity to power “house” loads like running lights, electronics, cabin lights, 12 volt appliances and other loads. To make the correct selection, we recommend that you first create an “energy budget” for your boat and then match your needs with batteries that contain the amp hour capacity and reserve minutes rating you need. For more on energy budgets and sizing “house” batteries, see our West Advisor article Sizing Your House Battery Bank.
Amp-Hour Capacity
Amp-hour capacity refers to the total amount of electrical energy a battery can store and supply over a period of time, typically measured in hours. For example, a West Marine Group 31 deep cycle battery with 105-amp hour capacity can theoretically supply 1 amp of current for 105 hours, 2 amps for 52.5 hours, and so on. It is important to note that the actual amount of time a battery can supply power will depend on the amount of current being drawn and other factors like temperature and age of the battery.
Flooded batteries, like this Group 27, offer dependable performance and are the least expensive option.
Reserve Minutes
Reserve Minutes is an industry standard that defines how long a battery can sustain a load of 25 amps before it drops to 10.5 volts at 80°F. Here is where it gets interesting: Under under this definition, how many available amps do we have if we take the 105 amp hour Group 31 battery mentioned above (that has a reserve capacity of 185 minutes) and place it under a 25 amp load at 80°F? Answer: 185 ÷ 60 = 3.08 hours. 3.08 hours x 25 amps = 77.08 amps — which is a far cry from the battery's 105 amp hour rating. What accounts for this? Without getting too technical, this can be explained in terms of Peukert's law which describes how a battery's voltage will drop comensurate with the load load placed on it. The point here is that the entire rated amp hour capacity of the battery will not be available to power house loads, which is why for flooded, AGM and gel deep cycle batteries, we recommend 3–4 times your daily energy consumption in battery amp hour capacity. This recommendation is aimed to ensure you avoid damaging deep discharges, and to reduce your recharging time. Note: Due to the extremely low internal resistance of lithium iron phosphate batteries, nearly all of their rated amp hour capacity is available to power house loads.
Choose a starting battery with the cranking amps you need.
To crank over an engine, starting batteries are designed to release a large number of amps over a short period of time. CCA is the number of amps a battery can deliver for 30 seconds at 0°F while maintaining its voltage above 7.2 volts. MCA is similar but measured at 32°F instead of 0°F. The reason that MCA are 20–25% higher than CCA is because batteries work better at higher temperatures. CCA ratings were originally used in the automotive industry. Since very few boats are used in sub-zero weather, MCA is a more realistic rating to go by. We suggest you consult your engine’s owner’s manual to determine if a battery’s MCA rating adequate to crank over your engine.
Flooded Lead-Acid Batteries
Based on proven technology that has changed little since the days of our grandparents, flooded lead-acid batteries are the least expensive battery chemistry. While they are reliable and can provide plenty of power, flooded batteries require regular maintenance, such as checking the electrolyte levels and topping off with distilled water.
The pros and cons of flooded lead-acid batteries are summarized below.
Pros:
- Cost the least compared to AGM, gel and lithium
- Handle overcharging better than AGM, gel and lithium
Cons:
- Produce hydrogen gas when charging, so battery boxes and compartments must be vented to allow gas to escape safely
- Must be periodically inspected and topped-off with distilled water when cell levels get low
- Self-discharge at relatively high rate of six to seven percent per month, so require off-season charging
- Must be installed in an upright position
- Do not tolerate high amounts of vibration
AGM Batteries
Many boaters are switching to AGM (Absorbent Glass Mat) batteries for a performance improvement over flooded batteries.
AGM batteries offer excellent shock and vibration resistance.
The construction of AGM batteries consists of positive and negative lead plates that are sandwiched between fine, highly porous microfiber separators that absorb and hold the electrolyte, which (like flooded batteries) is a mixture of water and sulfuric acid. The sandwiched construction provides more plate support and better shock and vibration protection compared to flooded batteries.
Unlike flooded batteries which release hydrogen gas (which can be explosive) along with oxygen, AGM batteries have internal pressure valves which allow oxygen produced on the positive plates to migrate to the negative plates and recombine with the hydrogen, producing water. This design allows AGM batteries to be completely sealed and maintenance-free.
Also unlike flooded batteries, which are offered in different versions for starting, deep cycle or dual-purpose use, the chemistry of AGM batteries enables them to function equally well for engine starting and deep cycle applications.
The pros and cons of AGM batteries are summarized below.
Pros
- Sealed, maintenance-free design
- Do not emit dangerous hydrogen gas to atmosphere
- Can be mounted in any position
- Up to twice the cycle life of flooded
- Excellent shock and vibration resistance
- Lower internal resistance allows greater starting power and charge acceptance
- Work well as dual-purpose batteries for deep cycle and engine starting applications
- Low 3% monthly discharge rate
Cons
- Higher cost compared to flooded
- More sensitive to overcharging compared to flooded
Gel Batteries
Gel batteries offer greater cycle life compared to flooded.
Gel batteries are a type of sealed lead-acid battery that uses a gel electrolyte instead of liquid. They are similar to AGM batteries in terms of maintenance requirements, but can be more expensive. Because gel batteries are primarily designed for deep cycle applications, they are not a good choice for engine starting applications. In addition, compared to AGM, flooded or lithium, gel batteries typically perform better with slower rates of recharging, so they are not a good choice for boaters who need rapid recharge times to get back on the water.
The pros and cons of gel batteries are summarized below.
Pros:
- Sealed, maintenance-free design
- Greater cycle life compared to flooded
- Tolerate deep discharges better than flooded
- Sealed design eliminates need to add water or check electrolyte levels.
- Spill proof and can be mounted in any position.
- Low 3% monthly discharge rate
Cons:
- Higher cost compared to flooded or AGM
- Can be damaged by exposure to high temperatures
- Not optimal for engine starting applications
- Recharge at a slower rate compared to other battery chemistries.
Lithium Iron Phosphate Batteries
RELiON's HP series of batteries are true dual-purpose batteries for engine starting and deep cycle applications.
Lithium batteries are the newest and most expensive type of battery but offer multiple advantages. Compared to flooded, AGM and gel batteries, maintenance-free lithium batteries weigh the least, have the longest lifespan, can be recharged more quickly and can be discharged to a very low state of charge without damage. In addition, compared to other battery chemistries, lithium batteries deliver more usable amp hours over their life compared to flooded, AGM or gel. In addition, the extremely low self-discharge rate of lithium means you don’t have to keep them on a charger during the off season like lead acid.
However, of the four battery chemistries, they are the most susceptible to damage due to overcharging, hence require charging systems with a lithium battery charging profile.
The pros and cons of lithium batteries are summarized below.
Pros:
- Longest lifespan of any marine battery type
- Tolerate deep discharges better than other battery types
- Compact and weigh less compared to flooded, AGM and gel batteries
- Can be recharged much faster than flooded, AGM or gel
- Produce more usable amp hours over their life compared to flooded, AGM or gel
- Extremely low self-discharge rate
Cons:
- Much more expensive than AGM, gel or flooded
- Require a compatible charging system to prevent damage
- Can be damaged if exposed to high temperatures
- Limited options for use as starting batteries
Battery Life in Charging Cycles
The useful life of marine batteries can be quantified in a limited number of charging cycles. A charging cycle is the combination of a discharge and recharge event. A standard flooded battery has a typical cycle life of 300 charging cycles. High-performance AGM batteries have a cycle life of around 500 cycles. For both flooded and AGM batteries, these figures are based on up to 50% depth of discharge which is a safe level of discharge for these types of batteries. Moving up in performance, gel batteries are capable of up to 75% depth of discharge and up to 500 charging cycles. Leading the pack in performance are lithium batteries which have a typical life of 3,500 cycles down to 80% depth of discharge. That is 7X more cycles than gel, 7X more cycles than AGM and nearly 12X more cycles than flooded!
The table below shows how the flooded, AGM, gel and lithium batteries compare. Prices are based on select Group 31 batteries as of 3/10/2023. For a deeper dive into how flooded, AGM, gel and lithium batteries compare, please read our West Advisor article Are Lithium Batteries a Good Choice for You?
| Battery Type | Depth of Discharge | Cycle Life | Usable Ah Over Lifespan | Battery Price* |
|---|---|---|---|---|
| Flooded Lead Acid | 50% | 300 | 15,000 | $205.00 |
| High Performance AGM | 50% | 500 | 25,000 | $383.00 |
| Gel | 75% | 500 | 37,500 | $510.00 |
| Lithium | 80% | 3500 | 280,000 | $1,160.00 |
Patrick Walters, Elite Series Pro Angler next to his RELiON battery installation.
So what is the best battery for you?
As we stated at the beginning of this discussion, the best battery for your boat is one that delivers the energy your boat needs at a price you can afford. Of course, this means different things to different boaters. For example, if you are a well-heeled cruiser accustomed to living your life afloat, a long term investment in lithium batteries, makes sense. Sponsored tournament bass anglers, who want to maximize the run time of trolling motors are another great candidate for lithium. However, if you are a day cruiser or coastal angler on a budget, lithium batteries would most likely be overkill. In this case, flooded, gel or AGM batteries may be the best choice for you.
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