Deep Cycle Battery FAQ

Sealed Lead Acid batteries are often referred to as being "maintenance free" or valve regulated. In a sealed lead acid battery the unit is sealed, meaning that water loss is kept to a bare minimum and also that you needn't put any water into the battery. Most of the sealed VRLA batteries are recombinant which essentially means that the water lost through the venting of hydrogen and oxygen in a flooded battery is the most common types of Sealed Lead Acid or SLA batteries that we carry are the AGM (Absorbed Glass Mat) batteries; another is the GEL type of battery.

AGM batteries have a very fine Boron-Silicate glass mat in between the plates inside the battery. The mats are about 95% filled up with electrolytes rather than completely saturated. The considerable advantage of this type of battery is that they can be operated in almost any orientation and will even function underwater. They will also never leak, even if punctured.

GEL batteries have the electrolyte stored in a gel form; this also won't spill out even if the batteries are broken and also prevents the stratification that other battery types can have. Gel cells, however, do have some limitations; they take a slower charge than a comparable sized AGM battery. If they are overcharged voids can form in the gel which permanently reduces the battery capacity.

For deep cycle applications however the Sealed Lead Acid type of battery can be a great deal more expensive than a comparable Flooded Lead Acid battery. However, there are times when a sealed battery will better meet your needs than a flooded battery would. Particularly marine applications where stability isn't always a given, and ventilated spaces are hard to come by are often well tailored to a sealed lead acid battery. One other advantage that AGM and Gel batteries have over flooded types is the low self discharge rate. Where a Flooded battery will lose about 13% of its charge in a month, a Gel or AGM will lose 1% -3%.

What are the differences between a starting and deep cycle battery?

Generally speaking, there are two different types of lead acid batteries, Starting and Deep Cycle. If a starting battery is routinely deep cycled (discharged below 20%-50% of max capacity), it will generally fail after 30-150 cycles. The same starting battery will last for thousands of cycles if it is just used normally (2% - 5% discharge).

• Starting batteries are generally designed to start some form of an internal combustion engine (car, truck, boat, etc). In a starting battery, you will find more lead plates, thinner and often made of a lead "sponge" similar looking to a foam sponge. This sort of arrangement means that the plates have much more surface area in the solution than a Deep Cycle battery and allow them to draw larger currents much quicker than a Deep Cycle battery.
• Deep cycle battery, on the other hand, have much thicker plates and, they are solid, not sponge. These thicker plates have less surface area and thus less of the instant power that a starting battery needs. They are designed to be discharged down to 20% of their maximum charge repetitively. The thicker lead plates allow for this as they are much sturdier than their sponge counterparts.
• Cold Cranking Amps (CCA) is an indicator of the amount of current a battery can deliver for 30 seconds at zero degrees Fahrenheit without dropping below a specified cutoff voltage (normally 10.5 volts). The cranking amps a battery can produce changes with temperature. The warmer it is the more Cranking Amps a battery will produce.

You can use a Deep Cycle battery as a starting battery provided that you take into account the lower CCA of a Deep Cycle battery. As a rule of thumb, it's a good idea to upsize the battery by about 20% to deliver the same amount of cranking amps from a deep cycle battery. Also, the self-discharge rate of Sealed batteries is a lot less than flooded lead acid types.

How long a battery will last depends hugely upon the way it is used and how well the battery is maintained. Both overcharging and undercharging will have serious adverse effects on the lifespan of a deep cycle battery. In particular, you can seriously shorten the lifespan of a battery if it is used in a deep cycle application that it was not designed for. An example of this would if you were to use an automotive starting battery as a deep cycle battery.

General expectations for batteries if deep cycled (these are just approximate guidelines):

• Starting battery (Automotive battery etc) : 3-13 months
• Marine Battery : 1-6 years
• AGM Deep cycle: 4-7 years
• Gel Cell Deep Cycle: 2-5 years
• Flooded Lead Acid Deep Cycle Battery (L16-RE etc): 4-8 years

The main things that you can do to ensure you get the maximum value out of your deep cycle batteries are to keep them maintained. This means keeping them watered to the appropriate level, trying to prevent them from discharging them more than 50% of their total capacity and having appropriate charging systems in place. The charging is of special importance because both over and undercharging will severely limit the life of your batteries, also if your batteries will see an extended period without being used you should ensure they are routinely checked, cleaned and fully charged before being stored. Also in some cases, it can be a good idea to put your batteries on a maintenance charge over long periods of disuse.

Battery Cycles vs. Battery Lifetime?

Often the lifespan you can expect to get out of your battery is referred to in terms of "cycles". A battery cycle is one complete discharge and recharge cycle. The discharge state of a battery is often measured in Depth of Discharge (DOD). This refers to how far down the battery has been taken, for instance, a battery that has 25% of its capacity remaining would be said to be at 75% DOD. The lifetime of a battery is directly related to the depth of the discharge that it regularly experiences. Lead acid batteries are fickle things. If you subject a deep cycle battery to 80% DOD on a regular basis you will get roughly half the life out of your battery than if you were to cycle it to 50% DOD. While this doesn't mean that you can't go down to 80% DOD you should generally try to design your battery banks to allow for cycling at around 50%. Conversely there is also an upper limit on the DOD of a battery, usually, a battery that is only regularly cycled down to 5% or less will not last as long as a battery cycled to 10% or more. This is because on smaller cycles the Lead Dioxide can clump up around the positive plates. On heavier discharges, this would be more of an even film.

What does Equalizing my batteries entail and when should I do it?

Equalizing a lead acid battery is the practice of applying a controlled overcharge in order to prolong the battery life, restore lost capacity and to make the battery more efficient. Batteries require equalization because as a battery is cycled (discharged and recharged) a small amount of lead sulfate remains on the lead plates. When you use a three stage charge the degree of sulfation is lessened, but not entirely eliminated. If this sulfate is left on the lead plates it will crystallize, once enough of these crystals have built up on the lead plates they can lead to lowered capacity and lower the amount of power the battery can produce. Also over the lifetime of a battery, the electrolyte solution can tend to stratify, forming layers inside the battery. This can cause the acid near the top of the cell to be more dilute than the acid at the bottom. An equalizing charge is essentially a controlled overcharging of the batteries which will allow the sulfate on the lead plates to recombine into sulfuric acid, it will also break loose any crystallized sulfate on the plates which will then fall to the bottom of the battery. It's always a good idea to not fill your batteries before you equalize, the electrolyte will expand during equalization and if the batteries are too full they could overflow. There should be enough liquid to cover the plates and not much more.

Below is a table from Trojan batteries website detailing their recommended charge levels and durations: