How Are Deep Cycle Batteries Rated? Explained For Dummies!

How can I determine how much power a deep cycle battery has?

Let's first explain what a deep cycle battery is. A deep cycle battery is designed to provide a steady current of power over a longer period of time without being charged or recharged as does a regular engine starting battery.

In one particular area of the battery construction, internally, in the plates, a deep cycle battery is very much opposite in design than an engine or starting battery. The significant difference is in the plate design and specifically in the thickness of the plates. Thin plates allow for a sudden and instant burst of power that can crank over a car engine for example. Thick battery plates allow for the opposite, for a slow but steady current of power over a longer period of time. This satisfies all those energy applications where there is no engine alternator to resupply charge back into the battery such as an electric golf cart where there simply is no engine!

Because a deep cycle battery doesn't need an alternator or any power source to supply charge while it is  in use supplying current while the engine is turned off it becomes a valuable source of power to many non-engine applications. It can discharge power for considerable lengths of time and be recharged back up later when a power supply source is available or provided. The deep cycle battery can and will discharge current to a deep level. The cycle is a discharge of current, deeply, and then later a re-charge to full charge state to complete one cycle.

We see deep cycle batteries in solar deployments, golf carts, floor machines, RV and Marine coach or house function roles and many other scenarios where there is no alternator to charge them in process while they are discharging power.

So, how can I determine how much capacity my deep cycle battery will give me? How do I know if I have enough power in my battery for what I am doing?

Let's start with rating.

Let's take a very standard deep cycle battery that has a 100 A.H. rating. A.H. stands for amp-hour rating. A.H. stands for amp hour and a battery that has 100 Amp hour capacity has a spec or listing as a 100 amp hour rated battery. This means the battery over the course of one hour can discharge or supply 100 amps. An amp is just a unit of electric current. At the end of that discharge when all those amps have been spent, that battery would be said to be 100% discharged. All the amp capacity has been spent. And, to charge it back up to full charge would complete a cycle. Keep in mind the general industry recommends not discharging your deep cycle battery below 50% as a regular practice as it will negatively impact the overall longevity of the battery.

So how much power can my 100 AH battery supply and for how long?

Two very popular rates to consider in the industry are the 20 hour and 5 hour rates. If we use the 20 hr rate then we would take 100 amp hours and divide them by 20 hour rate and we would get 5 amps and so that 100 amp hour deep cycle battery could steadily supply you 5 amps of power for 20 hours. If we want to determine the current we could get from the same battery at the 5 hour rate we would take the 100 amp hour battery rating and divide them by 5 and get 20 amps. In this scenario the battery would give you a steady current supply of 20 amps for 5 hours. So, if you took the 1 (hour rate) you would take the 100 amps and divide by one (hour rate) and yes, you guessed it, you would get 100 amps per one hour. 100 divided by 1 equals 100 amps.

Is it a good idea to spend or discharge out all my amp hours in one cycle?

Every battery manufacturer will advise you not discharge your battery fully in one cycle. The battery industry will recommend that you do not discharge your battery below 80% and furthermore if you are able to keep your batteries above 50% DOD (depth of discharge) regularly you will help to promote the overall longevity of your deep cycle batteries.

You can find deep cycle batteries at

Dec 29th 2018 The Battery Genius

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