In my recent research of batteries and battery type, I've found a lot of really useful information on the subject of a battery known as the deep cycle battery. For some preliminary information, a battery cycle is just a complete discharge and recharge, though not always discharging to 0%. A full cycle is most often a discharge down to about 15%-20%, and then all the way back to 100%. This helps determine the life of a battery. Battery life is determined by how deep the battery is discharged each time it's used and then recharged. This is called depth of discharge, or DOD.

Let's say a battery is discharged on a daily basis to half it's capacity, and another battery is discharged everyday to about 75% - 80% of it's capacity, and both are recharged each night. The battery cycled to 50% capacity will usually last about twice as long as the one cycled to 75% - 80% capacity. This relationship between depth of discharge and battery life continues all the way up to about 8% - 10%. If a battery is only discharged to 8% of its capacity each day and then recharged, it will last 5 to 10 times longer than a battery cycled to 50% of its capacity. But who wants to have a battery that they can only discharge 10% of the charge on before recharging it?

That's what's so handy about a deep cycle battery. Deep cycle batteries are designed to provide a steady amount of energy over a long period of time, and to be able to discharge a large percentage of their energy without overly depleting battery life. They're able to discharge 80% of their energy time after time and still have a large battery life. Similar in size and look to a standard car battery, a deep cycle battery has applications in storing and releasing solar panel energy (PV), marine boat operation, backup power, and running golf carts. Deep cycle batteries are generally the beating heart of solar power systems, allowing energy to be stored during the day for nighttime energy.

But you have to take care of your battery if you want it to last. Even having a deep cycle battery for your solar system isn't enough on its own to keep the system running without a hitch. Batteries, as you saw in the examples above, generally lose much of their charge and life due to user error in handling them. There are many factors that go into taking care of a battery. And now that more and more homes are going the way of solar and wind energy, it's important to realize the factors that cause battery life and charge to dwindle.

1) Temperature -- Extremes in temperature can quickly cause your battery to lose its life. Keep your deep cycle battery out of the sun.

2) Overcharging -- Batteries don't like getting charged once they've hit their max charge. You need to be careful not to keep pumping energy into them once they're fully charged.

3) Disuse -- This happens a lot with solar system batteries. Let's say you own a little cabin out in the woods of Minnesota that you like to go to for hunting. Being the ecofriendly environmentalist you are, you use solar power for the electricity of the cabin. But you're only there one month per year. That means that your battery isn't getting used 11 months of the year. That's an unhappy battery. Not to mention the extreme cold your battery probably has to face during the winter months when no one's around.

For a happy deep cycle battery, the best tip is to try and use half of its energy per discharge and then recharge it fully back to 100%. If you do this consistently, keeping your battery away from extremes in temperature, it will last you a very long time.  And this is a good thing, because the price of deep cycle batteries can get quite high.  Even the cheapest deep cycle battery is still around $75.

What causes a battery to lose its charge over time? The loss in charging and discharging power is due to something called internal resistance. Internal resistance is like the friction that a battery encounters when charging or discharging its energy. And just like the friction that happens when you rub your hands together, this internal resistance is also converted to heat energy. But friction in most things is usually bad. So, the lower the internal resistance, the better. Slower charging and discharging rates are more efficient. Loss of efficiency is usually in conjunction with a higher internal resistance at higher amperage rates.  This is good to be aware of because in the case that you're using your deep cycle battery for something other than solar energy storage, like say marine use, you'll have to get a deep cycle battery charger for it.  And these can be different.  It's my opinion that charging it slowly is the best way to go, so get a charger that can charge at low amps.

But there are other factors as well that influence battery life. Batteries come in all different sizes and shapes. Depending on the plate thickness of the positive plate, the type of battery, whether it's flooded, gelled, or absorbed glass mat (AGM), it can react differently to internal resistance and cycling. But that's all information for another article. The one thing I will talk a little bit more about is plate thickness. There's a term in battery life called "positive grid corrosion". In every battery, there are positive and negative metal pieces, like posts and plates. What happens during the natural life of the battery is that the positive plate starts to get eaten away gradually over time, even until there's eventually nothing left of it and it's reduced to sediment. So naturally, the thicker the plate, the longer the battery life will be. And this is a huge factor. Not having thick enough positive plates is one of the lead causes of battery failure.