This thread is intended as a repository for information about batteries and charging. If you know of a post or link that should be added, have a suggestion for something new, or notice something that needs to be changed in an existing post, PM John Jones or me and we will look into it.
Initially, discussions of Lithium Ion batteries will be limited because they differ greatly from other batteries and their use is currently limited. Gel cells are also skipped over because they have almost completely been replaced by AGMs in the bass boat world.
There are several specifications that determine how a battery will perform in a particular application. These specifications are measured using test methods that have been developed by battery industry and engineering groups in order to standardize the marketing and selection of batteries.
Cold Cranking Amps (CCA)
CCA is a rating of how much current the battery can provide at zero degrees F while maintaining a voltage of at least 7.2V. This is intended as an indication of how well the battery will perform in an engine starting application.
Marine Cranking Amps (MCA)
MCA is a rating of how much current a battery can supply at 32 degrees F while maintaining a voltage of at least 7.2V. MCA is almost never measured or tested, but is calculated by multiplying the measured CCA by about 1.3.
Reserve Capacity (RC)
RC is a rating that gives an indication of the performance of a battery with a steady, moderate current draw such as running a trolling motor or electronics and pumps. RC is determined at 80 degrees F by putting a 25A load on the battery and measuring how long the battery can sustain this load without its voltage dropping below 10.5V. When comparing RC, be sure that the testing on both batteries was performed at 25A. At least one major manufacturer puts 23A RC test results on their batteries.
Amp-hours are very similar to RC. Most Amp-hour calculations are for a 20-hour rate at 80 degrees F. For example, if a battery is rated at 120 AH, it can provide 6A for 20 hours without the voltage dropping below 10.5V. AH is a very good indicator of how a battery will perform in deep-cycle use, except manufacturers often use other AH ratings for the number on the battery label without indicating how it was tested. You are just as likely to see a battery with AH tested at the 20 hour rate as you are to see a battery with it tested at 1A. This makes comparison of AH ratings a little bit tricky.
How to Choose?
It would be nice if you could compare the numbers on the battery label and know which battery was better. Unfortunately, the numbers on the label donít always tell the whole story. Though there are battery testing standards, they are only guidelines and not laws. Fortunately there is a specification that does a pretty good job of allowing one to compare battery performance while shopping. This specification is battery weight. You canít produce power without plenty of good lead plates, and they cost money, so manufacturers arenít going to add more for no reason.
Most manufacturers adhere to the industry standards, but when in doubt, check the weight. If two batteries have similar specifications, choose the heavier battery. This is only valid when comparing the same technology batteries, so donít use it when comparing AGMs to flooded cells.
Anglers have three common options when it comes to battery technologies: Conventional Flooded Cells, Absorbed Glass Mat (AGM) and Lithium Ion. Like most things in life, each type has trade-offs.
Conventional Flooded Cells
These are the same technology that has been around for over 100 years. Lead alloy plates immersed in a solution of sulfuric acid and water.
These batteries are the cheapest of the three. Widely available at stores that operate seven days a week.
Potential for acid spills and splash out. Water may need to be added periodically to replace that used during charging. Self-discharge requires periodic charging during storage to prevent sulfation damage.
Absorbed Glass Mat (AGM)
AGM batteries are very similar to conventional flooded cells. The difference is that the space between the plates is filled with a glass mat which absorbs the electrolyte.
Pros: Low self-discharge reduces need for charging while in storage. Much less affected by sulfation than conventional flooded cells. Longer useful life. Generally more tolerant of abuse. Sealed construction allows for non-upright installation. Maintenance free.
Cons: Cost is about double that of an equivalent flooded cell battery. Charging requirements can require a new charger when switching to AGMs. With all else being equal, an AGM will be heavier than a flooded cell battery. Generally not as widely available as flooded cells.
Lithium Ion batteries are relatively new to the boating world. Their arrival was made possible by the development of LI technologies that were resistant to thermal runaway that presented an unacceptable fire risk in earlier types of batteries. Lithium Ion battery technology is significantly different from AGMs or flooded cells.
Pros: Substantially lighter than other battery technologies. Available in multiple voltages to allow one LI to replace two or three batteries of other technologies. Long service life.
Cost is nearly an order of magnitude higher than other batteries. Chargers are specific to LI batteries, but are often bundled with the batteries. Maintenance free. probably won't be available for local purchase.
For bass boat use, there are three primary demands on our batteries: Cranking the engine, running the electronics, accessories and pumps, and running the trolling motor.
Cranking batteries are optimized to produce a lot of current for a short period of time. This is done by maximizing the surface area of the lead plates inside the battery that are in contact with the electrolyte. A cranking battery will normally have a lot of very thin plates to give higher CCA. Cranking batteries are designed to work in an environment where they are recharged soon after use so they are maintained at full charge almost all of the time.
Deep-Cycle batteries are designed to survive being discharged deeply (30-80% depth of discharge depending on the technology) on a routine basis. Because conventional flooded cell batteries are subject to plate damage from sulfation and physical plate deterioration when operating under such conditions, deep-cycle batteries are generally built with thick plates. These thick plates limit the number of plates in the battery, which limits the ability of the battery to provide high current for starting applications. That doesn't mean you can't use a deep-cycle to crank an engine. It just means that you will need a physically bigger battery to provide the same CCA as a smaller battery designed as a cranking battery.
You may notice there was no mention of RC, AH or capacity in the paragraph above. Though RC is a critical specification for our boat batteries, RC isn't a characteristic deep-cycle batteries specifically. RC is mostly determined by the physical volume of electrolyte in the battery, not the type of battery.
If a lot of thin plates give you CCA, and thicker plates give you deep discharge tolerance, what do you get if you use plates thicker than a cranking battery but thinner than a deep-cycle? A dual-purpose battery. A standard dual-purpose battery is really just a battery designed to give reasonable service in mixed use situations.
All of what I wrote above is wrong!
Well, not really wrong, but it's out of date. Problem is that those terms and the battery design trade-offs are pretty well specific to conventional flooded cell batteries, but battery manufacturers and users use them to refer to AGMs and Lithium Ion batteries as well.
Most of the reason that you have to make the trade-offs between deep-cycle capability and CCA is the damage done to thin plates when a battery is deeply discharged. AGMs and Lithium Ions don't experience that problem to nearly the extent a conventional flooded cell does. That means they don't need the thick plates to tolerate deep discharges so AGM and Lithium Ion batteries are by nature all dual-purpose batteries.
So choosing a battery is easier than it used to be?
No, it's harder. Cranking the engine is no longer as simple as it used to be. The advent of computer controlled outboards has led to a requirement that the battery voltage stay substantially higher than the 7.2V used in the CCA test in order to keep the computer and sensors working during the engine starting process. Because the battery that cranks the engine is usually the same battery that runs live well pumps, anchoring systems and electronics, and it has to run all of this stuff without any help from the engine's charging system while we fish, the demands on our cranking batteries have become substantial. Not only does the engine battery need to provide a lot of CCA to crank a modern engine, it needs to have a high RC to run live well pumps, electronics and other equipment for long periods without the outboard running. This limits engine battery choices to a few larger AGM batteries for many bass boat owners.
When going with conventional flooded cells, you still need to pay attention to the deep-cycle/cranking battery distinction. Otherwise you just shop by CCA, RC and budget.
*There is more to it* The above neglects a few things which probably aren't of interest to most people. The specific gravity of the electrolyte and the particular lead alloys used in the plates also come into play with some of the discussions above, though not to an extent that the average person needs to concern themselves.
The term battery actually refers to a series-connected group of cells. The cells in a typical boat battery produce about 2.11V each, and are stacked six to a battery to produce the standard 12.6V to 12.7V battery. You can see the individual cells of batteries that have light colored cases, and, in the case of vented batteries, there is a fill hole on top for each cell.
A battery produces electricity by means of a chemical reaction. Two metal plates in a sulfuric acid solution undergo a chemical change to make electricity flow from the battery. The positive plate changes from lead peroxide to lead sulfate, while the negative plate changes from a porous “sponge lead” to lead sulfate. The sulfate comes from the electrolyte solution of water and sulfuric acid that becomes more and more water and less sulfuric acid as the oxygen leaves the positive plate to replace the sulfate in the electrolyte when battery is being discharged.
As we know, the chemical reaction in our boat batteries is reversible, and the opposite of the discharging process is charging. During charging, electricity is used to undo the chemical reactions that occur during discharge. The positive plate changes from lead sulfate to lead peroxide as the sulfate molecules go back into the electrolyte solution from the plates, while the extra oxygen molecules go back to the positive plates. The negative plate changes from lead sulfate to sponge lead, and the electrolyte solution becomes a stronger solution of sulfuric acid.
The charge discharge process is only reversible to a point. A small portion of the battery’s capacity is lost with every charge/discharge cycle. How much is lost depends on the depth of the discharge and how long the battery remains discharged.
You charge a battery by forcing current to flow through the battery. You force current through the battery by applying a voltage that is higher than the battery's terminal voltage to the battery terminals.
Though that is a simplified explanation, it's really not as complicated as charger manufacturers would have you believe. Most so-called "smart" chargers are little more than DC power supplies that monitor the current flowing into the battery and change their output voltage when they see the current is above or below a pre-determined level. Some have different voltage settings that the user selects when they choose what type of battery the charger is charging.
When it is first plugged in, a typical basic onboard charger functions as a 14.7VDC* power supply. It tries to raise the battery voltage to 14.7V, but that normally takes a lot of power if the battery is discharged very much. The charger is limited in the amount of current it can supply, so the charger may only be able to raise the battery to a lower voltage even when using all of the current it has available. Charger manufacturers like to say this is the constant current charging stage, but in reality it's just that the voltage doesn't rise to the set voltage because the charger doesn't have enough current to get it there. As the battery charges, the amount of current required to raise the battery voltage goes down, so the voltage slowly rises toward 14.7V while the current will stay right at the charger's rated maximum.
Eventually, the battery is charged to the point that the charger is able to supply enough current to raise the battery voltage to 14.7VDC. Once it reaches that point, the current drawn from the charger slowly drops, while the voltage stays steady at 14.7VDC. Charger manufacturers will call this the constant voltage stage, but in reality the charger isn't doing anything to change what is going on, and is behaving exactly like a standard DC power supply still.
When the current being drawn from the charger reaches about 1A, the charger switches over to float mode. This is the first time the charger has done anything to distinguish itself from a simple DC power supply. The charger will now switch over to float mode, a finishing stage, or in some cases turn its output off for a while. Float mode and finishing stages are just lower voltage settings. You'll normally see these operate at about 13.1 to 13.4VDC. A finishing stage is generally timed, with the charger switching to the standard float mode or shutting off the output after a fixed time. It's usually at this time that the charger indicates the battery is fully charged.
During float mode or shutdown, the charger isn't inactive. Float chargers continue to monitor the current into the battery, and if the current rises above 1A, the charger switches back to normal charging mode to recharge the battery. Chargers that shut down after charging generally wake up periodically and turn the output on to check the condition of the battery. If the current is below 1A, they go back to sleep. If the current is above 1A, the charger goes back to charging mode and recharges the battery.
During the charging process, most chargers have other things going on in the background.
Chargers monitor the voltage across their leads to see if there is really a battery there. If they can't raise their voltage to 2V or more, the charger assumes the leads are shorted and shuts down to avoid generating sparks that could cause a fire. This is the reason that deeply discharged batteries can't be recharged by onboard chargers.
Chargers monitor the current flowing through their leads. If they don't see any current, they assume there is a connection issue like a blown fuse, broken wire or lose terminal and shuts down.
Many chargers also keep track of how long it is taking to recharge the battery. If they can't raise the battery voltage to a certain level in a certain time, they assume there is a battery problem and shut down the charging process to avoid potential boat damage.
*This voltage varies depending on the battery type selected on the charger and the temperature.
Batteries sit there forever and nothing exciting ever happens, right?
Wrong. During charging, a battery produces hydrogen gas. Remember the Hindenburg? That was hydrogen gas, and it was probably just a small spark of static electricity that ignited it. It's very flammable stuff, and it is being produced in the same area where we are making electrical connections to our batteries. To make matters worse, the gas is contained in the battery case that happens to be filled with sulfuric acid. A spark produced by making or removing a wire or a defective plate within the battery can cause the battery to explode and shower the area and you with sulfuric acid and shards of broken plastic.
Getting sulfuric acid on your skin or all over your boat or garage is bad enough, but your eyes are particularly vulnerable to both the acid and the projectiles. Always wear safety glasses or goggles designed for working around liquids when working on or around a battery. Your regular glasses aren't good enough.
The second major risk when working with batteries is burns. Though the voltage the battery produces presents almost no risk of electric shock, the current provided by a typical battery presents a real danger. A typical wall outlet in your home provides 20A at 120V or about 2400W maximum. A battery can pretty easily produce three or four times that amount of power. If something shorts across your battery terminals, there is no fuse, breaker or switch to shut off the power and metal object like a wrench can be welded to the terminals as soon as it touches them making it very difficult to remove because it is stuck and will be orange hot in a matter of seconds. Donít wear jewelry when handling battery connections. A ring or watch across the terminals of a battery will seriously burn you. This isn't sunburn serious. This is skin grafts and loss of limb serious. To make matters worse, a shorted battery can get hot enough to suffer structural failure allowing plates to go where they aren't supposed to go. That can cause sparks and the battery can explode. Not a pretty picture.
When working on a vehicle or metal hulled boat, you should always remove the ground lead from the battery first. In most cases this is the negative lead*. Even though bass boats don't typically have a ground, the hull of a metal boat is likely to be unintentionally connected to at least one battery's negative terminal through the outboard, trolling motor or other equipment in contact with the hull. On a multi-battery trolling motor setup, you should remove the negative lead to the trolling motor before removing any connections from any of the batteries. This practice is best because if the wrench you are using accidentally touches the chassis or hull it could create a short an/or produce a spark. Nothing good can result from this. Once the grounded cable is removed, contacting the hull or chassis with the wrench on other terminals won't cause any problems.
*On some older vehicles the positive battery terminal is grounded.
Jumping a battery is the process of adding a second battery to a circuit to provide extra current to the starter. Jumping a battery is inherently a risky thing to do because you have to make connections from a good battery to a battery that is either deeply discharged or in poor condition.
When jump starting a vehicle, you make the positive connections between the positive posts of the two batteries first, while being careful that the negative cables don't contact either vehicle. Next make the negative connection to the good battery's negative post while making sure the other end of the negative cable doesn't touch either vehicle. Last, connect the remaining negative cable end to bare metal on the disabled vehicle as far from its battery as you can. This process is intended to make sure any sparks that occur happen away from either battery.
Things are a little different on a boat. You still need to be sure the cables don't touch anything but what you intend for them to touch, but you have no choice about making that last, spark creating connection, right on the battery terminal. Your risk of bad things happening is higher because of this.
When using a trolling motor battery to jump start your outboard, you need to take special care when choosing which battery to use. The safest thing to do is to remove all of the connections to a trolling motor battery and use that battery to jump start the outboard. Sometimes that isn't practical because of time or conditions. When jumping to a TM battery that is still connected to the trolling motor, jump only with the trolling motor battery that is connected to the negative feed to the trolling motor. This prevents inadvertently creating a short across one of your TM batteries because of unintentional hull connections or wiring that has been added to reduce TM noise in boat electronics.
If the cranking battery is deeply discharged or damaged, jump starting may not work because of the load created by the bad battery. If this happens, you may need to remove the cranking battery from the circuit and connect a TM battery in its place. There is no problem doing this, but don't try to swap the batteries back once you get the outboard running. Doing so can easily cause damage to the charging system of your outboard.
We're going to discuss a few basic terms about electricity that will help you understand and troubleshoot simple electrical problems in your boat. Electricity as we use the term in vehicles and boating is simply the flow of electric charge from one point to another.
Voltage represents the charge difference between two places. That can be the difference between the positive and negative terminal on a battery, or between the earth and the moon. Voltage represents the force that makes electric charge WANT to move from one place to another. At 12V, charge will flow if you give it a good path, but at 50,000V, charge will jump out and fly through the air if you give it a little opportunity.
A key thing to remember about voltage is that it is always relative. Voltage means nothing if given for a single point. I can say "The voltage of my thumb is 5,000V." Though my thumb is 5,000V above something somewhere, failing to say what the second place is makes my statement meaningless. It's similar to distance in this respect. If someone asks where you are, the answer "12 miles" means nothing. "12 miles north of your house.", however contains a little more information.
In discussion, the second point is often implied, but unless you understand that, you can be misled by readings and numbers. When we say "My trolling motor connector is at 36V.", what we really mean is "My trolling motor connector is at 36V above the voltage at the negative battery terminal."
You can think of voltage as the thing that compels electric charge to move from one place to another place.
Volts are also referred to as "potential difference" and electro-motive force.
In the discussion of voltage above, we call it a force. When thinking about a force, you need to realize that a force doesn't always cause movement. If lean into my truck and apply a force to it, it might move if it's in neutral and the brake isn't on, but if either of those things aren't released, it might just sit there. Voltage is the same way. Just because there is a voltage difference between two points doesn't mean anything is happening.
Current is the measurement of what is happening. Current tells us how much electric charge is moving between two points. Current depends on both the voltage difference between the two points and how easy it is for electric charge to move from on point to the other. That previous sentence is fundamental to understanding electricity, and is a simplification of what is know as Ohm's Law. The idea of how easy it is for charge to move from one point to another is called resistance.
Sometimes it helps to think of voltage and current in terms most people already understand. Think of a garden hose with water flowing through it.
The garden hose is the wire.
The pressure in the hose is the voltage. (Note how pressure is relative too. 30 psi actually means 30psi above the pressure outside the hose)
The amount of water flowing through the hose is the current.
If you have a big hose, and low water pressure, you get a decent flow of water.
If you have a low resistance wire and low voltage you get some current.
If you increase the water pressure, you'll get more water flow.
If you increase the voltage, you'll get more current flow.
If your hose is smaller, even with lots of water pressure you can't get a lot of flow.
If your wire has a lot of resistance, even with lots of voltage you can't get a lot of current.
Here is a key concept that explains a lot of problems in our boats:
"If your hose has a kink in it, the pressure will be lower after the kink than it is before it unless you have the nozzle on the end of the hose closed."
Think about that for a minute. If you put a kink in the hose while the nozzle is open, you will see the flow drop. If you put a kink in the hose while the nozzle is closed, what happens when you open the nozzle? When you first open it water will flow normally, then it will reduce to the level that the kink allows. That's because with no water flowing out the end of the hose, the pressure on both sides of the kink equalized.
This is analogous to a bad connection in wiring.
"If your wire has a bad connection in it, the voltage will be lower after the bad connection than it is before it unless you don't have any current flowing in the wire."
This last scenario is called "voltage drop", and is an important concept in troubleshooting boat wiring problems. The "bad connection" can be a rusty connector, undersized wiring, corroded wiring or a loose connection. Any of these makes it hard for current to flow. Current only flows when you have something on the end of the wire using power. A wire with no current flowing will be the same voltage from one end to the other. When something starts using power, then there will be a voltage drop at any poor quality connection in the path.
The term short or short circuit is commonly misunderstood. A short circuit isn't a loose wire. A short circuit won't cause strange operation or intermittent things to happen. A short circuit is a direct or nearly direct path from one battery terminal to the other and results in high current flow. If there is a fuse or breaker protecting a wire with a short, the fuse or breaker will blow or trip and the short is gone. If there is no fuse or breaker, something will burn if a short circuit occurs.