Battery Basics – Difference between a Starter and Deep-cycle Battery

News regarding solar energy generally focuses on solar panels, but without a battery to store the power collected from solar panels, much of the energy collected is fed into the grid for others to use. If the system is off-grid, that excess energy is wasted and there is no power to draw on when the sun goes down. A battery bank allows you to maximize the efficiency of your system and to have power to draw from 24-7.

Batteries come in two broad classifications: Starter and Deep-cycle Batteries.

Starter Batteries output large amounts of power for a short period of time.  These batteries are commonly utilized in starting vehicles or motors, with each use only discharging a large burst of current for a very short time. It is then recharged by the alternator for the next engine start. The emphasis of starter batteries is on power, not storage capacity. A serious weakness of starter batteries is that they aren’t built to endure deep-discharge or prolonged use. This will quickly shorten the battery life. Starter batteries have a very low internal resistance, which gives them the ability to crank out a high power load for a second or two. This low internal resistance is achieved by using very thin, sponge-like lead plates inside the battery for maximum surface area. The very thin plates are damaged or destroyed if subjected to steady continuous discharge. Generally, starter batteries are less expensive than deep-cycle batteries, but they are not interchangeable, despite the temptation.

Deep-Cycle Batteries (aka Marine Batteries) are essentially the opposite of starting batteries; they provide a consistent flow of current over long periods of time. They are optimized for capacity rather than short bursts of power. They have sturdy, thick lead plates that can better stand up to repeated discharges and recharges. Their ability to deeply discharge and to re-charge efficiently is needed for stable power supply to run equipment, appliances and act as utility-grade power. Deep-cycle batteries can be charged from a variety of sources. They charge using DC power from solar, hydroelectric or wind power or from an AC source; plug-in grid power or a gas fueled generator, that is then converted to DC charging power.

Important things to note in deep-cycle batteries are the Capacity, measured in Amp Hours (Ah) and the Cycle Life, which is the number of times the battery can be charged and discharged before it looses significant capacity.  The Cycle Life is depends on how deeply the battery is discharged on average. This is called the Depth of Discharge (DoD). Standard DoD for comparing deep-cycle batteries is the cycle life at 50% DoD.

It should also be noted that the warranties on most starter batteries are voided if you use them for deep-cycle use and that the warranties on most deep-cycle batteries are voided or substantially reduced if they are used as starter batteries. There are also some larger, heavier specialty deep-cycle batteries that are made to be used as both starter and deep-cycle batteries.

Deep-cycle batteries are used in home energy storage to store solar, hydro, and wind power, RVs and marine use for boondocking and power away from shore, off-grid homes, cabins and cottages, to run equipment, and to support mobile and portable power needs.

There are many different chemistries and points of comparison between different types of deep-cycle batteries which we explore in upcoming blogs.

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