Deep cycle batteries are the backbone of the solar power industry for a reason: they can store a lot of charge. Because they are designed to be discharged and charged over long periods, they are ideal for use in solar panels and renewable energy storage. They can also be used in campers and boats where you need to store power to use off-grid.
As with any battery, what you can and can’t run off depends on its amp-hour rating, the voltage of your system, and whether or not the device you want to run is a draw-on power. Lithium deep cycle batteries and Lead Acid deep cycle batteries can also be discharged differently.
What Does a Deep cycle battery mean?
A deep cycle battery is a battery designed to be regularly discharged and recharged. Unlike a starter battery, a deep cycle battery is designed to withstand repeated deep discharge cycles. A deep cycle battery is typically used in applications where sustained discharge over long periods of time is required, such as in electric golf carts, marine applications, and forklifts.
How far to discharge a deep cycle battery
A deep cycle battery can be discharged up to 90% however for lead-acid batteries it is recommended to only discharge them up to 50%. This ensures that the battery last longer. This is one of the biggest differences between lithium and lead-acid deep cycle batteries.
However, the amount of charge that a battery can provide depends on its C rating. Amp-hour is the rating used to rate how much amperage a battery can provide for exactly one hour.
Deep cycle batteries will have info on the Ah rating at multiple C ratings. A battery’s C rating is the maximum amount of current that a battery can safely provide. The rating is given in amps and is typically abbreviated as “C.”
Batteries will be imprinted with numbers like 0.1C, 0.2C, 1C, C10, and so forth. These indicate the C rating of the battery. “C” rating is used as battery power can not be discharged all at once the time is a factor when discharging batteries to ensure safe use.
For example, 12V100Ah battery, C is 100. “1C discharge” means 100A as discharge current. And just like that, 0.1C is 10A, 0.5C is 50A, which equals the number before C multiplied by the C value.
Deep cycle batteries are usually rated at 0.2C and are meant to be discharged over a 20hr period.
How Many Amp-hours in a Deep Cycle Lithium Battery
A lithium-ion battery can provide more amp-hours that a lead-acid battery of the same capacity. This is because as mentioned before a lead-acid battery can only be discharged up to 50% while lithium-ion batteries can go up to 90%.
This, therefore, means if you have two 100Ah batteries; one lithium and the other lead-acid you can only get 50 Ah from the lead-acid battery while the lithium-ion battery can deliver 90 Ah.
Lithium-ion batteries also charge faster and can go through many cycles of charge and discharge in a single day, therefore, providing even more capacity. This is why lithium-ion batteries are replacing lead-acid batteries in many applications. Generally to get the same runtime as a Lead-Acid battery on a Lithium battery you just need 60% capacity of the Lead-Acid battery you are replacing.
Li-Ion also has the capability to discharge at higher rates than other types of rechargeable batteries because it doesn’t generate heat while being discharged so it can still provide full power even at lower voltages.
How Long will it hold a Charge When Not in Use?
A lithium-ion battery can last up to 6 months when not and will only discharge partially. This is because they have a low discharge rate. This is compared to lead-acid batteries that will not go beyond 30 days and you have to use a battery maintainer to keep the battery alive.
A lithium-ion battery and specifically a LiFeP04 battery should last more than 10 times longer compared to other types of rechargeable batteries under normal use conditions.
LiFePO4 battery cells also have a longer life cycle, up to 5000 cycles while the lead-acid batteries are typically around 300–500 cycles
Amp-hours to Watt-Hours
Amp-hours and watt-hours are both units of energy, but they are not interchangeable. Amp-hours are a measure of charge, and watt-hours are a measure of power. To convert amp-hours to watt-hours, you need to know the voltage of the system.
Multiply the voltage by the number of amp-hours, then divide by 1000 to convert to watt-hours. For example, a 12 volt system with 20 amp-hours of charge would have 240 watt-hours of energy (12 x 20 = 240, 240 / 1000 = 0.24).
Deep cycle vs Starter Batteries
A deep cycle battery can be used continuously for hours and recharged over a fairly short period of time. A starter battery is made to provide a burst of amps in a short period of time to start an engine. Once the engine has started the alternator takes up the job and there is no more draw on the battery.
How to Tell a Battery is a Deep Cycle
Starter batteries like the one in your car have a large number of thin plates comprised of a lead sponge. This provides a very large surface for the electrolyte to react providing a big draw of power.
A deep cycle battery on the other hand is characterized by thicker and fewer plates. There is less surface to react with the electrolyte so the current release is slower therefore ideal for a steady draw.
On the other hand, all Lithium-ion batteries are deep cycle batteries no matter the physical characteristics as they can be discharged up to 90%.