A deep cycle battery is any battery that has been specifically designed to be regularly and deeply discharged. That means, unlike a standard starting battery like you might have in your car, a deep cycle battery is intended to be discharged by up to 50%, or in some cases as much as 80%.
Understanding the difference between a deep cycle battery and a starting battery will help you know what kind of power supply you’ll need to bring with you if you’re planning to go camping, off-roading or even boating.
In this article, we’ll explain what you need to know about deep cycle batteries and answer some common questions.
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Why do I need a deep cycle battery?
If you’re planning to do anything that requires power over a sustained period of time, you need a deep cycle battery. A great example of this is camping — you’ll bring your car or truck out with you, and might also bring appliances like lighting, a camping fridge or entertainment devices. You might think you’d be alright to run these devices off your car’s battery, but you’d be likely to run into trouble by doing so.
A starting or SLI (Starting, Light, Ignition) battery is designed to deliver a large amount of energy in a very short burst. This is what happens when you turn on your ignition. The battery activates, delivers power to the engine, and the engine and alternator take it from there. Only a small amount of the power in the battery is actually used, and it’s not good for the battery to be discharged below 80% of the maximum charge.
Your power needs for camping or boating are different from that of your car. The energy required is often much lower, but over a much longer period of time. For this, you need a deep cycle battery. These batteries are specifically designed to deliver slower, steady power and can discharge to a much lower level. Deep cycle batteries can also be easily recharged using solar panels or by being connected to a charger plugged into power mains.
What should I look for in a deep cycle battery?
All deep cycle batteries are rated in amp-hours. An amp hour is, simply put, the number of amps a battery will discharge over an hour. Amp-hours are calculated by multiplying the number of amps pulled by the number of hours the battery was in use. So if something pulls 20 amps over half an hour (0.5), then the amp-hours would be 10.
You will normally see the amp-hours of a deep cycle battery listed as “20 HR”, or 20-hour rate. In this case, the battery’s power output has been measured over a 20-hour period. For a deep cycle battery with a 100 AH 20-hour rating, the battery was discharged with a 5 amp load over those 20 hours.
Simply put, the higher the 20-hour rating, the more power a battery can supply over a 20 hour period. Of course, this doesn’t guarantee a deep cycle battery will last 20 hours, particularly if the amp load is higher.
So, when buying a deep cycle battery, consider the amp load of the items you intend to use the battery with. On average, a portable fridge-freezer will use about 1-4 amps per hour, depending on the outside temperature. This could be anywhere between 20 and 80 amps per 20-hour period. In this case, a 100 AH deep cycle battery will usually have you covered. It doesn’t hurt to have some extra charge in reserve however, so if in doubt, go for the highest 20-hour rating you can.
Note that a deep cycle battery, though designed to be discharged far more than a starting battery, still should not be completely emptied as this will shorten the battery’s total lifespan.
The different types of deep cycle batteries
There are a variety of deep cycle battery types. The one you choose will depend on where and how you want to use it.
You can shop Marshall batteries different deep cycle battery ranges here:
Heavy Industrial Cycling
Semi-industrial Cycling
Orbital Sealed Deep Cycle and Starting
AMP-Tech Deep Cycle
Flooded lead acid batteries
Flooded lead acid batteries are the oldest style of car battery in use. Though often used as starting batteries, flooded lead acid models can also be made as deep cycle batteries.
A deep cycle flooded lead acid battery usually has a usable capacity of up 50%. This means that once the battery is down to 50% of its total charge, it will need to be recharged.
If you’re budget conscious, you might consider a flooded lead acid battery as they tend to be affordable and reliable. That said, they do have much shorter lifespans than their alternatives and require the most maintenance.
Absorbent Glass Mat (AGM) batteries
AGM batteries are a higher quality alternative to flooded lead acid batteries. Their name refers to thin fibreglass mats that are placed between the lead plates. These mats absorb electrolytes, stopping them from moving and spilling and acting as a damper between the two plates.
In addition to a 50-80% depth of discharge and 95% charge efficiency, AGM batteries are maintenance free, able to withstand shock and vibration and charge much faster than flooded batteries.
Note that AGM batteries can be sensitive to overcharging, so it’s important to use a regulated charger.
Gel batteries
Gel batteries are a great option for application in high-heat environments. These batteries use a gelled electrolyte, usually formed from sulfuric acid and water, suspended in silica.
You can expect about 75% depth of discharge for a gel cell battery, and charge efficiency around 85-90%.
Gel cell batteries are maintenance free, spill-proof and insensitive to high heat, movement and positioning. Note that gel cell batteries don’t tolerate fast charging and are sensitive to overcharging, so it’s critical you have the right charger.
Lithium ion batteries
Lithium ion batteries are relatively new technology, and offer a more lightweight alternative to gel and AGM batteries. With 80% depth of discharge and nearly 100% charge efficiency, lithium ion batteries perform well above their weight.
They’re also likely to charge faster, have a longer lifespan, and deliver constant voltage until discharged — no dimming lights as the battery drains.
With the above benefits and the same freedom from maintenance and high durability of AGM and gel cells, lithium batteries have a lot to offer. On the flipside, they’re far more expensive than their alternatives.
Need a new deep cycle battery?
Before you head out on the water or to the campgrounds, be sure you’re equipped with the right battery to see you through your trip. Check out our extensive range of car battery replacements here. Marshall is here to help. Holler for a Marshall on 1300 627 742 or contact us online for a new battery quote.