Deep-cycle solar battery is your energy storage and backup in case of an emergency. Its lifetime can go over 10 years or it might not even reach 6 months. It all depends on the battery maintenance and how you treat it. These simple tips should help you to extend its lifespan.
Lead-acid batteries should be charged as soon as an opportunity presents itself. Using a partially-charged battery leads to sulfation: lead-sulfate inside a battery crystallises and it can no longer be charged. Partial state of charge, however, is less of a problem for lithium-ion batteries.
What's more, you shouldn't use a fully-charged battery in conjunction with a partially-charged one. The loss of electrical energy goes along with the gain of thermal energy, but an empty battery has higher resistance and heats quicker. If one battery is charged and the other is not, but you're running them as a single unit, you risk overheating the second one to the point of no return.
Battery charge level can be checked via a charge controller or manually with a voltmeter. For example, the voltage of a fully charged 12 V battery should be around 12.6 V. When its load is down to 50%, the voltage is closer to 12.3 V — a sign that it has to be recharged. When the battery is at approximately 20%, its voltage drops to 11.5 V. Voltage also rises, when the battery is being charged: for example, a full battery in a charging state is going to show 14 V, but this number drops after it is disconnected from a charger.
Every 15 °F above 77 °F halves the lifetime of a battery
High temperatures drastically shorten the lifetime of a battery. The normal operating temperature for batteries is 77 degrees °F. According to data of Sandia National laboratories, every 15 °F above that mark is going to halve the lifetime of a battery. For example, your battery should last for six years on paper. If the weather in your area heats up to 85 °F on a regular basis, expect it to last for about three years. When the temperature gets really high, it can even provoke an internal explosion of a battery. Cold temperatures affect deep-cycle batteries in another way: the capacity of a battery drops and it needs more current to be charged.
Buying a battery and saving it for a rainy day is honestly not a great idea. Batteries don't like not being used: it shortens their lifespan and decreases efficiency. Therefore, if you have a battery, you better put it to work. However, sometimes there is simply no use for it. Before storing it, charge it fully and disconnect all cables. Put a battery in a cold place (not too cold) and give it a boost once every two months or so.
Lead-acid battery depth of discharge (DOD) is usually around 50% and it's not recommended to discharge it further on a regular basis. For example, a battery that is always discharged by 80% can survive up to 250 cycles. If it was discharged only by 50 %, it could handle up to 750 cycles. Lithium-ion batteries have a much bigger DOD which reaches 80-90%, but a full discharge should be avoided with any battery you have.
A part of flooded deep-cycle battery maintenance includes refilling it with distilled water every two weeks. Distilled water can be substituted with deionized water or at least water whose ratio of T.D.S. (Total Dissolved Solids, parts per million) doesn't exceed 200. Remember that plates of a battery should not be exposed to air, because it leads to corrosion. At the same time don't fill the battery all the way to the top — it needs just enough electrolyte to cover the plates. Check out our article on the history of batteries and the basics of their functioning.
3-6 years
Average lifespan of a deep-cycle lead-acid battery
Equalization is the process during which you charge your deep-cycle battery with very little flow of current. This process takes more time than normal charging and aims to make sure every cell in the battery gets charged equally. Such a procedure might sound complicated but chargers for batteries and charge controllers can be set specifically to perform this task. Equalization should be performed every 1-3 months for deep-cycle batteries, both lead-acid and lithium-ion — check the instructions for your particular battery model for more details.
The layer of dust that forms on the battery is itself capable of creating an electrical pathway. While it's hardly dangerous, it causes the current leakage in your battery and your accumulated energy goes in vain.
Whenever you use a battery in a solar panel system, it's almost mandatory to add a charge controller for safety reasons. A charge controller:
• protects the battery from high voltage of panels;
• prevents its overcharging;
• stops the use of the battery in a partial-charge state;
• blocks the reverse currents, which can occur at night when the electricity flows from • battery back to solar panels.
There are two main types of controllers: PWM (pulse width modulation) and MPPT (maximum power point tracking). The first type is cheap, the second one is efficient. Read more about controllers in our article.
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Corrosion isn't a rare occurrence with batteries and can be harmful. It can be cleaned with the paste of baking soda and distilled water:
• use a wire brush to apply the paste;
• let it sit for a while;
• clean and dry your battery with a paper towel or cloth after you are done;
• apply a thin layer of silicon dielectric grease afterward.
It's also a good idea to watch the connections: they should be fixed tightly at all times.
Lead-acid batteries are almost obsolete: consider switching to lithium-ion ones. They can be counted as deep-cycle by default and therefore they're perfectly suited for solar panel systems.
Lithium-ion batteries are lighter, more efficient, require less maintenance than lead-acid batteries and have a higher DOD. There's no need to water them and they are less susceptible to partial state of charge. Just as lead-acid batteries, they don't like high temperatures and prefer not to be fully discharged. Don't put anything flammable around them!
The biggest problem with lithium-ion batteries used to be their high price. However, in the last 10 years, it has dropped five times: from $692 per kWh in 2014 to about $133 per kWh in 2024, according to BNEF. The main reason is decrease in the cost of raw materials for energy storage. Experts believe that the prices may continue to drop. If you need a recap on different types of deep-cycle batteries, check out our article.
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Andrey had been a news editor and freelance writer for a number of medias before joining A1SolarStore team. Climate change and its impact on people's lives has always been among his interests and it partially explains his degree in Philosophy and Ethics.
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