FAQ Deep Cycle Battery

Deep Cycle Battery Information

Bateries for Solar Power

How To Calculate Specific Gravity

Charging Deep Cycle Batteries

Deep Cycle Maintenance Guide

Wiring Batteries In Series

Wiring Batteries In Parallel

Wiring Batteries In Series Parallel

What is a "Flooded Lead Acid" battery

The most common type of deep-cycle battery is the wet cell battery, also known as flooded lead acid. In contrast to a sealed battery, the water lost through gassing in a wet battery can be replaced by end users using vent caps on top of the battery. Floating batteries have been around for a long time, but have remained popular because they offer cheap prices and good performance. There is generally twice as much money for a gel or AGM battery per amp hour as there is for a flooded battery. Due to the fact that flooded batteries do not have a recombinant structure, a lot more maintenance is required, since water gets lost through the vent caps while charging. Adding new water to your battery can be time-consuming, but it is necessary if you want to get the most out of it.

What is a "Sealed Lead Acid" battery (VRLA's)

Batteries that utilize sealed lead acid may be described as "maintenance-free" or valve-regulated. Sealing ensures minimum water leakage in lead acid batteries and without the need to add water to them. We offer a range of sealed lead acid (SLA) batteries. The A8 type of sealed battery is the most common, including the premium GEL and the A9 type.

What are AGM Batteries?

Between the two metal plates of an AGM battery is a delicate glass mat made of Boron-Silicate. There are still about 95% of electrolytes left in the mat, but they are less saturated. These batteries appear to be the most flexible option because they are able to be operated in nearly any orientation and can even function underwater. Also, even if punctured, they will not leak.

What are GEL batteries?

A GEL battery has the electrolyte in a gel form, which is also very resistant to spilling out even if the battery is broken; this also prevents the accumulation of chemicals that can occur with other battery types. While gel cells are, however, less efficient than their AGM counterparts in terms of charging, they do come with some limitations. Gel batteries can suffer permanent damage if overcharged, as voids form in the material.

The cost of sealed lead acid batteries for deep cycle applications will be much higher than a flood cell. You will, however, find seal-cell batteries perform better than flooded-cell batteries in certain situations. Sealable lead acid batteries are well suited for marine applications where stability isn't a given and ventilated spaces aren't always available. Additionally, the AGM/Gel batteries have a lower self-discharge rate than flooded batteries. The charge of an AGM or Gel battery will lose 1% to 3% within a month versus 13% on a Flooded battery.

What would be the differences between a starting and deep cycle battery?

It is generally understood that lead acid batteries fall into two categories, starting and deep cycle. The life of a battery whose discharge is frequently below 20%-50% of maximum capacity tends to be shortened for at least 30 to 150 cycles. As long as you use your starter battery normally (2% to 5% discharge), it will last for thousands of cycles.

An internal combustion engine (car, truck, boat, etc.) in general is meant to start with a starting battery. Batteries that are meant for starting contain more lead plates, typically thinner and made of lead "sponges" similar to those found in foam sponges. The plates on a Deep Cycle battery, by comparison, have much less surface area and can only draw large currents much slower than plates on a Standard battery.

However, deep cycle batteries are much thicker and have solid plates, as opposed to sponge. Since they have a smaller surface area, thicker plates do not provide as much instant power. This allows a constant discharge to a maximum of two percent of their charge. It is possible due to the thicker lead plates which are much stronger than their sponge counterparts. The Cold Cranking Amps (CCA) are indicative of how much current a battery can produce at zero degrees Fahrenheit for 30 seconds without dropping below a specified zero-voltage cutoff voltage. A battery's capacity to crank amps is changed by temperature. As the temperature rises, the more Cranking Amps a battery is able to generate.

A starting battery that has a lower CCA is suitable for a Deep Cycle battery but it should be taken into account. According to rule of thumb, to achieve the same cranking amps from a deep cycle battery, you should increase the size of the battery by about 20%. A sealed battery suffers from lower self-discharge rates than flooded lead acid batteries.

What's the life expectancy of my battery?

Batteries often last for long periods of time based on how frequently they are used and how efficiently they are maintained. Undercharging and overcharging a deep cycle battery will both lower its lifespan considerably. If a deep cycle battery is used in an application for which it was not intended, it is likely to suffer a serious shortening of its lifespan. The automotive starting battery can be used as a deep cycle battery, as an example.

The typical performance of deep cycle batteries (these are just guidelines)

  • AGM Deep cycle: 4-7 years
  • Flooded Lead Acid Deep Cycle Battery (L16-RE etc): 4-8 years
  • Gel Cell Deep Cycle: 2-5 years
  • Marine Battery : 1-6 years
  • Starting battery (Automotive battery etc) : 3-13 months

Keep your deep cycle batteries well maintained if you want to get the most value out of them. It entails carefully monitoring their water distribution, preventing discharges greater than 50% of their capacity, and ensuring that charging systems are in place. In addition to properly charging your batteries, to make sure they will last as long as possible, you should check your batteries routinely, clean them, and charge fully before storing them to prevent overcharging or undercharging. A maintenance charge can also be beneficial when the battery is not being used for a prolonged period.

The Battery Cycles vs The Battery Lifetime?

In battery talk, you often hear about "cycles" to describe the lifespan of the battery. During a battery cycle, the battery is completely discharged and recharged. Batteries are often measured by their Depth of Discharge (DOD) in order to determine their discharge state. A battery that has 25% of its capacity left is considered to be at 25% DOD. Similarly, if a battery has 75% of its capacity left, it would be at 80% DOD. How deeply a battery is discharged consistently determines its lifespan. Battery life is fickle with lead acid batteries. Deep cycle batteries subjected regularly to 80% DOD will only get half the life as batteries subjected to 50% DOD. However, you should try to design your battery banks to allow for cycling at around 50%. While you can go down to 80% DOD, you should generally try to avoid it. In addition, the cycle life of a battery is limited as well, typically, the battery that is cycled regularly down to a 5% or lower DOD will not last as long as a battery cycled up to 10% or more. Lead Dioxide can accumulate around positive plates on smaller cycles since it can clump up. A lighter discharge would create a more even film.

Battery Gel Battery Cycle Life vs Depth of Discharge

Why do I need to Equalize my batteries?

Equalization involves applying a controlled overcharge to lead acid batteries in order to prolong their life, restore capacity, and make them more efficient. In batteries, equalization is necessary since the lead plates remain coated with lead sulfate after cycling them (discharging and recharging). Sulfation is diminished, but not entirely eliminated, when you use a three-stage charge. It can result in a reduced capacity and lowered amount of power if this sulfate crystallizes on the lead plates. An electrolyte solution in a battery can also degrade during its lifetime. Equilibrating a battery is essentially charging it to overcharge it in order to cause sulfate to recombine into sulfuric acid on the lead plates, breaking loose any crystallized sulfur on the plates. When you equalize your batteries, you shouldn't fill them too full, as the electrolyte will expand during equalization, and if you fill them too much, the batteries could overflow. Not much more should cover the plates than should be in the fluid.

Before you equalize your batteries, remember the following:

Any DC loads should be disconnected from the batteries to prevent damage to anything connected during the equalization process. The higher voltage that occurs during equalization may lead to damage. Cap the cell; the caps provide ventilation and prevent electrolyte from splashing onto the top of the battery. Another precaution that can be taken is to lay a paper towel over the tops of the batteries. The charging process should be stopped immediately if a battery begins to "spit" acid. You should equalize batteries that have been fully charged and at room temperature.

Equalizing steps:

  • It is best to use flooded acid batteries that are fully charged, at an even temperature, and is properly insulated
  • Remove any load from the batteries
  • Connect the charger
  • Chargers should be set for the proper voltage
  • You should start charging your batteries
  • Eventually, the batteries will start gassing and bubbling
  • Make sure you take specific gravity measurements every hour or so
  • In the gassing stage, gravity is equalized when it ceases to rise

Do I need to refill my batteries? How often should I do so?

The longevity and performance of flooded batteries can be enhanced by watering them periodically. Gases escape from the vent caps while chemical reactions happen. Therefore, the battery's acid will eventually weaken until it's beneath the level of the lead plates. The good news is, as only water is lost (hydrogen and oxygen), it only has to be pure water that needs to be replaced.

You may need to add water to your batteries more or less frequently depending on the temperature and how frequently you charge them and discharge them. If temperatures rise or cycling occurs more frequently, watering will need to occur more often. If you haven't used your batteries for awhile, it is a good idea to top them off a few times every month until you have an idea as to how thirsty they are. If you refill your batteries, you should use deionized or distilled water. Water from a tap infected with minerals and chemicals can weaken batteries and increase the rate at which they self discharge. It may be advantageous to consider a battery watering system if your batteries are heavily used or in a spectacularly awkward position.

Connected to a battery vent hole, they snap into place. Filling your battery is a simple process that requires only the connection of a water supply rather than spilling. I like it better than the normal method because it takes much less time and requires less clothing.

How do I calculate Specific Gravity?

A battery's specific gravity is measured by comparing its weight to the weight of an equivalent volume of water, which is commonly referred to as the Specific Gravity ratio. A cell's particular gravity is measured with a hydrometer, which makes account for temperature when determining specific gravity. A hydrometer measures the density of the electrolyte with each change in water/sulphuric acid in the battery. This will occur because the proportion between water and sulfuric acid in the battery changes with activity. With the Specific Gravity testing, you should also take a look at your battery's Open Circuit Voltage.

Charging a Battery

In order to charge a lead acid battery, three stages are required. It is because some chargers have three stages of bulk, absorption, and float that they are called 3-Stage.

The Bulk Charge:

Battery charging begins with this first stage. A charger does not send more current than the cells can safely handle, but rather the maximum voltage in addition to that. Voltage varies between 10.5 and 15 volts, but in general this ranges from that to the next volt or so. At this point the battery has been recharged to around 80% to 90% of its capacity.

Absorption Charge:

As the internal resistance in the battery increases, the voltage of the battery becomes constant during this second phase of charging. Here the charger generally produces the maximum voltage possible, which is typically around 14.5 to 15 volts.

Float Charge:

The battery voltage drops to around 12.8 to 13.2 volts when it reaches its maximum charge during the absorption phase of charging in order to reduce gassing and prolong the battery's life. The battery must be correctly charged during this stage, sometimes called "maintenance charge," even when the device is not being used, so that it will be able to function at its maximum capacity when needed.


There is a wide array of chargers available; a cheap charger, when used incorrectly, will do more damage to the battery than a quality, three stage charger. A three-stage charger has many safety features and prevents current from flowing until a battery is connected and connected correctly. Besides being fan cooled, they may also come with features such as automatic temperature control and short circuit protection. Other battery chargers, however, do not generally come with access to the safety features described above, nor will they automatically shut off or lower the voltage once the battery gets past the bulk charging stage. If this sort of charger is left unattended, your battery may suffer long-term damage or even be critically damaged. Before charging deep cycle batteries, make sure you've read the manual and taken the proper precautions.

Regularly checking the voltage of your batteries will give you a good idea of their charge:

FAQ Deep Cycle Battery Chart

It is essential to take specific gravity readings to obtain precise information about charge state.

Which type of capacity do I need? What is an "amp hour"?

Amp-hours are used to measure battery capacity. For a twelve volt battery, it is when the battery reaches 10.5 volts when it is discharged that the amperage is measured. To calculate the Ah rating, multiply the amps by the time taken. In other words, if you had a device that was pulling 25 amps and you used it for 30 minutes, you would have used up that much amp-hours since 25(amps) x 0.5(hours) = 12.5 amp-hours. Deep cycle batteries are rated for 20 hours, which happens to be the most common rating period. This shows that 20 hours of testing had brought the battery down to 10.5 volts and the total amps it provides were measured. It is important to understand that sometimes the time period does differ, and if the amp hour rating is 6 hours in some circumstances, and 100 hours in others, that could be useful. It is known that a battery's amp hour rating increases the longer the battery is discharged. For example, the capacity of the Trojan T105-RE is 225 at 20 hours and 250 at 100 hours.

Are batteries affected by temperature?

Lead acid batteries vary with the temperature in which they operate. The capacity or life expectancy will therefore vary. Heat causes batteries to work harder and last shorter, but also increases their capacity. Additionally, when the temperature drops, the battery's capacity decreases but it lasts longer. Around 20% lower capacity of batteries exist at freezing temperatures, and around 12% higher capacity at 122 degrees F. The charging voltages for battery cells start at 2.7 volts per cell (for a 12v battery) at -40c and drop to 2.3 volts per cell (13.8 volts for a 12vol battery) at 50c. Temperature correction is built into some charge controllers.

Is there a memory effect with a deep cycle battery?

Lead acid batteries do not have a memory, in fact it is important to note that completely discharging lead acid batteries can greatly shorten its shelf life.

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