Ways To Charge Deep Cycle Batteries

Deep cycle battery charging guide.One of the worst ways to lose performance on a deep cycle battery, or any other type of battery for that matter, is incorrect ways of charging. Fortunately, learning how you can charge a deep cycle battery properly is fairly easy, and this article aims to make you familiar with the steps involved in such task.

Battery Types

First of all, let me talk about battery types. There are different classes of these portable energy sources, and each classification carries with it a specific definition. Batteries are classified in two ways: first, in the way they are constructed (construction class); and second, by what they are used for (purpose or application class).

Now, there are a lot of ways to construct different batteries, but there are three major ones that deserve to have their own classification type. These are gelled, flooded (or “wet’), and sealed AGM (or “Auto Glass Mat”).

You can also classify AGM as “starved electrolyte” or “dry” type batteries because its fiberglass mat (from which the name was derived) has no excess liquid — it is only 95% saturated with sulfuric acid. So when you hear people say that they need a “dry” battery, they most probably are referring to an AGM type battery.

Flooded batteries, on the other hand, may have removable caps and at the same time can be classified as “maintenance-free” batteries. This is because these types of batteries are designed to be disposed after the warranty has expired. Rarely do these types of batteries last one week after the warranty expiration.

Meanwhile, AGM and gelled batteries also called valve regulated batteries because they have a valve that keeps the pressure in the battery slightly positive. Sealed batteries are the same, and they are commonly referred to as “valve regulated lead acid” or VRLA batteries.

As for major purpose classifications, there are three: automotive, marine, and deep cycle. Deep cycle batteries, the focus of this article, include those that power boats and RVs. Backup power and solar electric power systems are part of the deep cycle class, as well.

Hopefully, from these descriptions, you can determine what type of battery you are working with. You can also check what kind of batteries best fit your purpose.

Deep Cycle Charging Stages

Deep cycle batteries in particular have three stages or “periods” of charging. These periods are called bulk, absorption and float charge stages. The bulk charge stage is where its maximum current rating is sent while also trying to maintain a constant voltage running throughout the battery components. This eventually turns into the absorption stage, wherein the battery gradually lowers in voltage while the internal resistance is building up.

Upon reaching full charge, the battery reaches the float stage. The charging voltage is reduced in the float stage, and the battery will be maintained by what is called a “trickle” charge. In float mode, the only purpose is to prevent a fully-charged battery from discharging, so it “trickles” charges in to keep up with whatever minimal energy loss the battery is experiencing.

It should be noted that solar chargers accomplish float state charges by checking voltage drops on the battery and sending a “pulse,” accordingly. A pulse in this case means a short charge cycle, enough to make up for the momentary energy loss experienced by the battery. In float stage, these pulses can occur anywhere from thirty to one hundred time per minute.

Deep cycle AGM batteries are special in that they do not experience as drastic a discharge rate compared with lead acid batteries. However, to prevent lasting damage to the battery that may mar its performance, a reliable float state charge is still needed. Regular maintenance and energy top up is key for the longevity of these batteries. So charging deep cycle batteries or any other type of battery, in general, involves three main tasks.

First of course is getting charge into the battery, that’s a given. But chargers need to optimize the charging rate as well, so that charging time would not be very long. Basically, this means being able to efficiently recharge the lost energy in just a short amount of time. Finally, chargers must also detect if the battery has reached full charge, and then stopping if it is so. It may also enter into the float or “trickle” stage when necessary.

Nowadays, smart chargers can efficiently help you with these tasks. A solid advice is to look for one with a “reverse pulse” technology, as this type of smart charger can do all those task, plus it can also regulate the temperature to avoid overheating. But if you do not have the luxury of a smart charger, just make sure that the charging current is just about 10 percent of the amp hour rating of a flooded lead battery. This can go up to 30 percent on an AGM lead cycle battery.

Charge time

Charge time is a variable feature, and it all depends on the charger and the battery capacity. The reconstitution of the battery charge is taken at a steady time, so as to maintain a safe temperature and to avoid overheating or overcharging the battery. A good rule of thumb when determining charge time is to find out two things: the capacity of your deep cycle battery and the charge rate of the charger you are using.

For example, a charger that puts out ten amp per hour would take approximately ten hours to charge an empty 100-amp deep cycle battery. Overcharging may be less of an issue in smaller devices, but there is a greater risk in deep cycle batteries. It is important to monitor the charging process to avoid this issue. Among the risks involved is grid corrosion, which can severely reduce the life of the battery.

What’s more, if there is excessive heat on the battery plates, it will cause them to buckle and then shed their active material. This is another reason why smart chargers are a must, because this type of charger can automatically turn itself off when it detects that the battery is on a full level of charge.

Solar charging

Deep cycle batteries can also be charged using power from the sun. This has the advantage of charging the battery even if you are away from the mains power, so you cannot really go wrong with investing in solar panels that will help you with this task. Plus, after the initial expense, all the energy you get afterwards is FREE, barring some maintenance costs.

Of course, once you obtain your solar charging system, you need to set up the panels so that they can get ample sunlight. After this, they will need to be connected to a solar regulator, which is also known in some circles as a solar “charge controller.”

The charge controller is really important! Do not even attempt to set up a solar charging station without it. This is because the 12 volt solar panels will give off fluctuation amounts of energy, and this unstable energy transmission can severely damage the battery if left unregulated. The solar regulator will help keep a steady stream of energy towards the battery.

Some solar charge controllers can also detect when the battery is full. When this is the case, the controller automatically switches the charge state into float mode, so the threat of overcharging is eliminated.

You can also check two related articles below!

Article1: How Many Watt Solar Panel To Charge Deep Cycle Battery?

Article2: Best Deep Cycle Solar Battery Tips

The Lifespan Of Deep Cycle Batteries

how long does deep cycle battery last?Whether you like it or not, you cannot really deny that batteries have a fixed lifespan. The longevity of a battery varies from type to type, but deep cycle lifespan is typically determined by maintenance, temperature, and the way it is charged.

There are newer batteries that do not even last a year because of water loss and overcharging, while there are used ones that went on to serve 35 more years because it is well-maintained.

However, if the ideal conditions are met, deep cycle batteries have approximate lifespans depending on their intended purposes. For example, Marine deep cycle batteries lasts 1 to 6 years, while those used in golf carts can last 2 to 7 years. AGM deep cycle batteries can last anywhere from 4 to 8 years. The deep cycle L-16 types, a popular one, can last 4 to 8 years, while a Rolls Surette premium deep cycle battery can survive for 7 to 15 years.

Deep cycle batteries used in heavy industrial work can last for 10 to 20 years. Interestingly, Nickel iron and nickel cadmium batteries can last for up to 35 years if maintained and charged properly. Minimum lifespan for these types is just about 5 years, though. (If you would like to save money buying the battery, then check this useful article).


As mentioned earlier, learning ways to charge deep cycle batteries, or any other type of battery, for that matter, is essential for the longevity of these portable energy mediums. There are other maintenance steps one can take to prolong the life of an energy cell, but knowing how to properly charge (and never overcharge) can go a long way in maintaining the efficiency of your energy sources.