What are amp hours on a deep cycle battery, what is a dual purpose/deep cycle battery?

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vector illustration of two men are of different opinion with empty speech bubbles

When you are considering the best deep cycle batteries for your boat or RV, there are a couple of questions that you should know the answer to. The first is: What are amp hours on a deep cycle battery?

You don’t want to get a battery you can’t use to its potential. Another question we will answer is: What is a dual purpose/deep cycle battery?

Knowing the answer to these questions will help shed some light on the basics of deep cycle and dual purpose/deep cycle batteries.

What are amp hours on a deep cycle battery?

Amp hours refer to how many amps a battery will put out over a specified amount of hours. This information can be especially useful if you want to get a battery that will put out a specific number of amps to run a trolling motor or other auxiliary equipment like on an RV.

This rating is specifically used on deep cycle batteries. While other factors exist in choosing a deep cycle battery, this one helps you evaluate a battery’s performance for your needs.

How are amp hours calculated?

Amp hours are calculated by multiplying the amp output of a battery by an amount of time. While this may seem simple, it is important to know that the amp output could be measured over five hours, 20 hours etc.

The most common span of time for amp hour ratings is 20 hours. When looking at amp hours, the listing should specify the span of hours used in the rating.

The actual amp hours rating will likely be listed in the following format:

  • Amp Hours {AH}: 100 AH at 20 Hour Rate
  • Amp Hours {AH}: 90 AH at 20 Hour Rate
  • Amp Hours {AH}: 75 AH at 20 Hour Rate

Remember that the AH number is the amps multiplied by the 20 hour rate.

If the listing doesn’t specify, make sure to investigate further. We have provided some more confusing listings below.

  • 92 ah MCA 900 CCA 580
  • 105 ah MCA 1000 CCA 800

The last two listings provided were actually taken from a dual purpose/ deep cycle battery. The AH is listed but the time span is not in these specifications.

This leads us to the next question:

What is a dual purpose/deep cycle battery?

Dual purpose batteries have the capabilities of performing two important battery functions. A dual purpose/deep cycle battery operates at a low amp level to run electrical components, but also has the cranking amps to start an engine.

A dual purpose/deep cycle battery does have an AH rating which should help you determine if it will suit your needs as a deep cycle battery. It also has ratings for a starting motor in the form of cold cranking amps (CCA) or marine cranking amps (MCA).

Why can’t I just use a regular battery for a deep cycle?

Most of the equipment that would require a deep cycle battery, especially older equipment, could get burned up by a regular battery. Some suggested reading material that could shed more light on the subject can be found in this article about boat battery basics.

Amp hours and their significance when looking at deep cycle batteries cannot be overlooked. Make sure the amp output of a deep cycle battery will suit your needs when picking one out.

While deep cycle batteries come in many different AH ratings, there are also other factors that will go into getting the right one.

Dual purpose/deep cycle batteries also offer some advantages when using two batteries is just not an option. The AH rating also applies to dual purpose/deep cycle batteries so be sure to check to see it suits your needs.

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