When it comes to solar power, you need high-quality batteries that can provide reliable power. These batteries should have good discharge rates and can be re-charged quickly.

These characteristics are especially important for people who live off-grid or in recreational vehicles.

Deep cycle batteries are commonly used for solar power. There are various types of batteries that can be used for this type of power generation.

We will also touch on the pros and cons of the main types as well as briefly answer a few commonly asked questions about deep cycle batteries.

What is a deep cycle battery?

A deep cycle battery is designed to have a high depth of discharge. This feature allows it to store more electricity and provide a steady stream of power.

Deep cycle batteries are also commonly used for marine applications. They can be used for various electrical appliances such as air conditioners and microwave ovens.

Although deep cycle batteries are commonly used for marine applications, they should not be confused with starter batteries.

A deep cycle battery is also known as a dual purpose battery. It can be used as a starter and a continuous power source.

What is the difference between a deep cycle and a regular battery?

Compared to a regular car battery, a deep cycle one has a denser active material and a thick plate structure.

Types of deep cycle battery

In terms of capacity range, there are two: 6 volts and 12 volts. Of these, there are 3 basic types used for solar, which are:

1. Flooded lead-acid battery

This type of battery is usually made up of lead-acid or grid-type components. It is usually made up of concentrated sulfuric acid.

Due to the heavy weight of the battery, its popularity has been declining.

Being the cheapest and oldest battery technology, it has been popular among the budget-conscious and practitioners of off-grid living.

Pros and cons of flooded lead-acid batteries

Pros:

  • Cheapest type of deep cycle battery
  • Reliable
  • Low internal impedance
  • Can deliver very high currents
  • Tolerant of abuse and overcharging
  • Indefinite shelf life if stored without electrolyte
  • Can be left on trickle or float charge for prolonged periods
  •  Available via many suppliers worldwide
  • The world’s most recycled product

Cons

  • Very bulky
  • Very heavy
  • Typical usable capacity of 30 to 50%
  •  Charge efficiency of 70 to 85%
  • High self-discharge, 5% per month
  • Can fast charge
  • Can overheat during charging
  • Generate poisonous gases when charging
  • Require regular maintenance to top-up electrolyte
  • Low cycle life – about 300 to 500 cycles
  • Must be stored fully charged to avoid damage
  • Must be kept upright to prevent electrolyte spillage
  • Sensitive to freezing (case bursts, electrolyte spills)

2. Valve Regulated Lead-Acid (VRLA) battery – Gel and AGM

This type of battery is created to overcome the issues associated with the flow of liquid electrolyte (FLA). Instead of flowing freely, the VRLA has a thick electrolyte.

There are two types of VRLA batteries: gel and absorbed glass matt. The former has a gelled electrolyte and the latter uses an electrolyte in a glass mat.

Pros and cons of gel deep cycle batteries

Pros

  • No maintenance
  • Low self-discharge (1 to 3% per month)
  • Charge efficiency of 85 to 90%
  • More tolerant of high heat than AGM
  • Gelled electrolyte (silica added) does not spill as easily as flooded lead-acid
  • Gel cells are sealed, so there is no risk of gas leakage or electrolyte spillage with typical use and charging

Cons

  • More expensive than flooded lead-acid and some AGMs
  • Cannot tolerate fast charging
  • Can be damaged by overcharging
  • Require own specific charging profile – different from AGM, lead-acid or lithium

3. Lithium-ion battery

Lithium batteries are commonly used in recreational vehicles. They are made up of a cathode and anode plates that are submerged in a solution of lithium salts.

Other categories of deep cycle batteries

1. Deep cycle marine battery

This type of battery has a heavier structure than a traditional deep cycle battery. It is usually made up of lead sponge plates instead of starting battery plates.

2. Group 31 deep cycle battery

This type of battery has a capacity range of 75 to 125amp hours. It is commonly used in various applications such as marine, automotive, and off-grid.

3. Group 27 deep cycle battery

Also large and powerful like Group 31, it has a slightly lower Amp hour range of 66 to 110 Ah. The application is similar to Group 31.

4. Group 24 deep cycle battery

The capacity of a deep cycle battery is divided into groups based on its size and description. These are assigned based on the size of the battery and its characteristics.

How to charge a deep cycle battery properly?

For a deep cycle battery to function properly, it needs a charging device that can match its charging profile.

The voltage points of the charging device should also be set to the correct values for each type of charging cycle.

How long does a deep cycle battery last?

It depends on a few factors but still less than factors than those of a lead-acid battery. They are:

  • proper maintenance
  • discharging and charging correctly
  • correct use during below freezing temperatures
  • temperature in the battery storage area

A more accurate way of estimating the life of a deep cycle battery is by charging cycle. It can range from 3 to 20 years depending on the model and the charging frequency.

AGM and flooded lead-acid batteries can last for up to 6 years. Gel batteries can last up to 20 years.

Can I connect different batteries together?

You can only connect the same type of deep cycle battery to the same charging device. The length and size of the charging device should also be the same.

Although the battery bank can be plugged into the RV’s engine starter battery, it should also be connected to a different part of the RV to allow it to be charged.

Conclusion

Although deep cycle batteries are ideal for solar systems in RV’s, their price can be a deterrent for people who are on a tighter budget.

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