How Long Should You Charge A Deep Cycle Battery?

Deepc cycle battery charging time is how long?Deep cycle battery charging is one of the most common activities nowadays, as it has become synonymous to giving life to cell phones, laptop computers, tablets, and other electronic conveniences that are commonplace in today’s world. Yet some people do not realize that charging has been an important part of life for decades before the advent of the internet, as automotive and marine vehicles require specialized batteries to start their engines.

In any case, it is is not surprising that charging time has improved through the years, and how long you should charge deep cycle batteries are no exception. There are many types of deep cycle battery and they are mostly used for marine or automotive purposes. However, this category of energy storage systems are so named because they are designed to operate even on deep discharge cycles.

This means that they work well even if discharged below 50 percent of their capacity. You might wonder how this makes them special, as cell phone batteries nowadays can go on a one percent discharge spree (seemingly) without any problems. But to actually understand why deep cycle batteries are special, one must know that there are battery types not designed to withstand such deep discharge cycles.

Starting batteries used in cars, for instance, only get their optimal lifespan if they are operated within a two to five percent depth of discharge before recharging. Also, it may seem that the batteries that power today’s smart phones and tablets may be okay with draining them to less than 10 percent discharge. But unless specified that they are okay with deep cycling, you may actually be shortening their life span by draining them too much without even knowing it.

Charging Times And Stages Of Charging

Charging times are easy to predict, in theory, but in reality there are many factors that contribute to the length of time it takes to fill a battery with energy again. This is especially true for deep cycle cells; they tend to have longer charge times because they allow for deeper discharge depths than most other batteries.

Bulk, Absorption, And Float

To better understand the rates of energy replenishment, we should take a look at the three stages of charging. These are the bulk stage, absorption stage, and the float charge stage.

The bulk stage is the first part of the charging process, wherein the maximum voltage is detected and transmitted to the battery while the charger tries to maintain a consistent voltage output all throughout the process. After some time that the battery is in bulk stage, the charging procedure will eventually lower in voltage as the battery moves on to the absorption stage.

The gradual lowering of the voltage is also the start of the increase in the battery’s internal resistance. When the battery receives its full charge, the internal resistance will be almost at its highest, and the voltage output from the charger will be reduced even further. This is known as the float stage, and this is also where the “trickle” or maintenance charging process usually kicks in.

The trickle or maintenance charge refers to a process wherein a specialized charger will output just about enough energy to refill what amount of energy the battery slowly loses naturally. It is a way to keep the battery from losing too much energy from natural discharge over time, for example when the battery will be placed in storage.

Charge Time Calculation

At the risk of stating the obvious, the total amount of charge time is the time it takes for a charger to refill the battery’s active cells with energy again, all while keeping the temperature at relatively safe levels— which means that charging batteries should not get too hot because excessive heat is a deterrent to healthy battery life.

To have an informed estimation of how long this will take, you basically need two factors: the amp hours of capacity that a deep cycle battery stores, and the amp rating of the charger you are using.

Estimating the charging time is a simple matter of dividing your battery’s capacity by the amp rating of the charger. Say for example that you have a deep cycle battery that has a capacity rating of 200 amp hours. Let me also say for instance that the current charge rate of this battery is about 50 percent, which means that it needs approximately 100 amp hours to charge it in full.

Now, let me say that you have a charger that can output 10 amps per hour —or put more simply, this is is a 10 amp hour charger. This means that it will take ten hours to refill the needed 100 amp hours of the battery in our example. 100 amps (the current discharged capacity) divided by 10 amp hours (the charging rate) equals 10 hours of charging time.

Obviously, this is a long time, and no everyone has the luxury of charging a battery overnight. This is why some people prefer a 20 amp hour charger, which will cut our hypothetical charging time by half, down to 5 hours. Fast chargers with a charge output of 50 amps per hour will bring that charging time down to 2 hours.

A word of advice regarding fast chargers, though: their use is generally not recommended. While chargers with lower amp hour output have slower times, these actually are preferable to overly fast charging processes. This is because the risk of overcharging is lower on slow charges, and overcharging contributes the rate of deterioration of battery performance.

The excessive heat produced by fast charging can make the plates buckle and the active material that touches the cells peel off and be shed. Plus, overcharging can cause corrosion in the battery grid. Basically, overcharging can shorten the lifespan of a deep cycle battery, so be careful with using fast chargers on them.

Features Of A Smart Deep Cycle Charger

Deep cycle batteries can avail of smart chargers to efficiently carry out these operations. Of course, the most obvious job of the battery charger is to get energy back into the cells for later use. But smart chargers can also optimize the charging rate for a more efficient procedure, plus they should also be able to sense if the battery is in full charge. They will stop charging if they detect that the job is done, so that overcharging will never be an issue.

There are also smart chargers that have a technology called “reverse pulse” that helps reduce the temperature of the battery while charging. A good rule of thumb when charging deep cycle batteries rated at 12 volts is that its current output must be around 10 percent of the amp hour rating for a flooded lead acid battery. Meanwhile, if you are using an AGM lead acid type, then you should consider increasing that value to up to 30 percent of the AGM’s amp hour rating.

Solar Power Charging

Refilling deep cycle batteries with energy collected from the sun is a very viable method of recharging. It is cost effective, too, as all you will need to spend on is that solar panel set up and a controller that will regulate the charging process. After this, you can get all the free energy the sun can offer. It offers an environment free solution to an energy problem that is saturated in petroleum and fossil fuel based energy sources.

A solar power controller is a must because the solar power panels do not produce a consistent and reliable voltage output. Most of them are rated 12 volts, but it is not enough to trust them to do the job alone because the prominence of the sun is factor. A solar controller can help stabilize the voltage output, keeping the battery receiving only safe levels when the energy collection goes overboard.

There are also solar chargers that have the ability to detect when the battery is full, and then switches to float charge stage automatically. Aside from the reduced risk of overcharging, it could also be that these kinds of chargers will provide a trickle or maintenance charge to keep up with the battery’s natural discharge rate.

Smart solar chargers do this by sending “pulses” to the battery, which can be described as short bursts of charging cycles. This miniature charging cycles can occur multiple times every minute. This makes this kind of smart charger and all around good choice and the only setback is for when the weather is bad.


I hope this article helped you learn about the different factors that affect how many hours you need to charge a deep cycle battery. There are stages in battery charging, which makes the process all the more organized in our heads, and helps us have a deeper understanding of what goes on in our batteries when we plug them in.

The parts describing the features of a smart charger can help you make an informed decision about what charger best suits your needs, be it traditional charging or one that uses an array of solar panels.