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Cranking battery failure is the most common reason emergency generators fail to start when needed. Ironically, cranking battery care and replacement is about the simplest and most inexpensive issue owners of emergency generators have to deal with.

Much of the problem has to do with confusion about cranking batteries. Maybe I can clear some of this up.

The public is barraged with misleading and false claims about batteries. Most of this creates fear of battery failure and results in increased battery sales. However, this misinformation often brings about failure of starting motors and starting systems as well as other equipment damage. Losses can be significant when emergency power systems fail due to battery troubles.

Tip - You get the best performance out of your cranking batteries when you do these four things:

1. Always record the date you install a new battery and replace the battery every three years without fail.
2. Float a 12-volt automotive battery at 12.75 to 13 VDC. Double this for 24-volt systems.
3. Keep the battery terminals clean and tight.
4. Always buy the biggest and heaviest battery that will fit the battery tray.

Our mission is emergency generator reliability. We do not care anything about batteries used to start vehicles, run trolling motors or lights in boats, start farm or garden tractors, or any other purpose other than emergency generator starting or stationary DC power plants. As a result we have become immune to the hype, advertising, ridiculous warranties, and false claims put forth by the sellers and manufacturers of automotive and marine batteries.

We look at batteries from a strictly scientific point of view. We know what they are and we know how they work. I will explain all of this later on in this service bulletin. For now, let me present a few points to keep in mind:

• No battery additives ever work.
• No mechanical or electrical devices intended to prolong the life of a battery ever work.
• Pro-rated warranties are worthless.
• Warranties are generally not indicators of the batteries quality.
• Batteries last about three years, after that they should be replaced. It is essential that you record the date whenever you install a new battery.
• Battery float voltage between 12.75VDC and 13VDC per six cell lead-acid flooded battery will deliver optimum life and reliability.
• It is not normal to ever add water to a battery.

Now, I'll explain all of that.

Pb=metal lead
PbO₂=lead dioxide
PbSO₄=lead sulfate
H₂SO₄=sulfuric acid

A standard 12-volt lead-acid flooded battery (automotive type like you use on your generators) consists of six cells. Each cell is made up of an equal number of negative (lead) and positive (lead dioxide) plates immersed (flooded) in a solution of 33% sulfuric acid and water. The cells connect to a bus that connects them in series to the positive and negative posts.

Each cell can produce approximately 2.05 volts. With the cells in series, the overall terminal voltage should be about 12.25 volts at rest with neither load nor charger connected.

When a load is connected, the metal lead (Pb) that makes up the negative plate reacts with the sulfuric acid (H₂SO₄) to form lead dioxide (PbO₂). The lead dioxide that makes up the positive plate reacts with sulfuric acid to form lead sulfate (PbSO₄). The sulfuric acid electrolyte breaks down into water, free sulfur, hydrogen gas, and oxygen gas.

In order for these reactions to occur, the lead atoms that make up the negative plate must expel electrons while the lead dioxide molecules that make up the positive plate must receive electrons. The resulting flow of electrons from negative to positive can be used to do work.

However, the work stops when enough atoms and molecules have been used up that the reactions cannot move forward. It is a lot like running out of gas.

When the terminal voltage is elevated, as with a battery charger, the reactions reverse. Lead dioxide on the negative plate becomes metal lead again; lead sulfate on the positive plate becomes lead dioxide; and the electrolyte mixture again becomes sulfuric acid.

Each time these reactions exercise, some components fail to return to their original condition. As a result, all lead acid batteries begin to fail the instant they are made. Eventually, age, heat, exercise, loss of fluid, and contamination along with other factors, bring about failure.

What is a battery designed to do?

Now that you know how a battery works, let's discuss what it can do. The battery will produce a constant flow of electrons over a period of time as the reactions progress. For example if you have a battery rated as 90-amp hour, that means it can produce 90 amps for one hour and maintain its minimum design terminal voltage.

If the minimum working voltage is designed to be 10 VDC, a healthy battery will deliver 90 amps for 1 hour and keep its voltage above 10 VDC. If it drops below 10 VDC the battery has lost capacity and should be replaced.

Keep in mind temperature is also a factor. Manufacturers usually design around 80 degrees F. When you discharge a battery at a temperature below its design temperature it will not perform at full capacity.

If a starter motor is designed to crank an engine and use 500 amps at 12 VDC while doing it, then a battery can be applied to match this load. Under these circumstances the simple formula of volts x amps = watts comes into play.

6000 watts represents the load. This figure will remain constant because the engine will always require a minimum amount of torque to crank over at its designed cranking speed.

(Actually the torque needed to crank the engine does change. However, we are going to pretend this doesn't happen because for now it would only complicate the issue and obscure the point)

The problem remains to not only find a battery big enough to provide the 500 amps, but one that will provide 500 amps long enough to go through three complete cranking cycles. Further, as the current is delivered to the starter motor, the terminal voltage will decrease. We don't want it to drop below 9 VDC. In fact, if we can find a battery that will keep the terminal voltage above 10 VDC the system will perform better.

The reason this is so important is the more current (amps) you draw through winding the hotter it becomes. It is the heat that damages the insulation on the magnet wire that makes up the windings in a starter motor. Too much heat will cause the motor to fail.

Remember the load remains constant, so as the voltage goes down the current will have to go up and create damaging heat.

Now you can calculate all of this, but that is the job of the engineers who design the systems. In fact, all of the necessary data is available to run the numbers, but the generator and battery manufacturers do not make it available to their customers.

The most expedient solution is to buy the biggest, heaviest, highest rated battery you can find to fit into the battery tray on your generator.

As if this isn't enough, there is one more thing to keep in mind. Batteries are rated in Cold Cranking Amps. Always buy the highest CCA rating at the lowest temperature.

For example 1040 CCA @ 32 degrees F is a better battery than 1040 CCA @ 80 degrees F and not as good as 1040 CCA @ 0 degrees F.

All chemical reactions become more active at higher temperatures. Therefore, a battery will produce more current at 80 degrees than at 0 degrees. When you buy batteries be sure to look at the temperature ratings. Keep in mind this is not scientific battery rating. It is just another piece of misinformation battery manufacturers use to confuse the issue and increase profitability. If you understand this concept you will get better value for your money as well as improved reliability from your generator.

PH
4-2-03