What is the Difference between Deep Cycle and Starter batteries?

While both deep cycle batteries and starter batteries are lead-acid batteries their uses totally differ and are different in how they are made. Lithium-ion deep-cycle batteries are more common nowadays. But in this article, we are comparing lead-acid types.

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.

A deep cycle battery isn’t suitable to start an engine as it may not have the burst of power needed to start the engine while deep cycling a starter battery can ruin it quickly and can only last for a few deep discharges (around 150).

Lead Acid Battery
A car battery

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. 

Deep Cycle Batteries | Image Courtesy of solarpowerworldonline

A deep cycle battery is the recommended type of battery to use in either a solar collector( photovoltaic), backup power, RV, or boat application.

  1. What is a deep cycle battery?

    A deep cycle battery is a battery designed to be discharged up to 80%. It is made up of thick solid lead plates compared to the thin plates of a starter battery (car battery). There is a lesser surface to react with the electrolyte so the current release is slower therefore ideal for a steady draw.

  2. Can I use a deep cycle battery for starting?

    A deep cycle battery is meant for slow constant discharge while a starting battery is made to provide the initial oomph to start the battery and then the alternator does the rest. You can use a deep cycle battery as a starter battery but you’ll have to oversize it considerably (by more than 20%) compared to what you are replacing or whatever is recommended.

  3. Difference between a deep cycle battery and a marine battery?

    The term deep cycle batteries is used interchangeably with marine batteries.  Most marine batteries are actually hybrids between deep cycle and starter batteries while a few are actually true deep cycle batteries.

    Deep cycle batteries are made up of thick plates that provide a small surface that reacts slowly for a steady draw.  A marine battery is made up of a lead sponge that is coarse and heavier than that of starting batteries. This makes it easier to make a huge draw like a starting battery while also being able to draw a steady current.

  4. What is the best way to charge a deep cycle battery?

    A deep cycle battery is made to be charged for a short period of time and discharged for a long period of time.  Therefore the best settings would be to bulk charge the battery and switch it to float after it's fully charged. A solar charger with a charge controller will provide a boost during peak sunlight hours and a float charge when the sun is going down without overcharging the battery.  

    This can allow you to draw power from the battery while charging and save enough power to use during the night.

  5. Can you use a deep-cycle battery in a car?

    Car engines require a large starting current to start the battery.  To use deep-cycle batteries in a car you need to considerably oversize the battery in order to get the same cold-cranking amps.  However modern cars do not really need as many cold-cranking amps as the old type of vehicles.

    Also, modern vehicles may fair better with deep cycle batteries as they have alarms and appliances that slowly drain the battery leaving it dead. 

  6. Does a deep-cycle battery need to be vented?

    The old type of flooded lead-acid batteries required venting but not all deep cycle batteries are flooded lead-acid batteries. You can also get Gel or AGM deep cycle batteries that use a different technology that does not require venting or maintenance. Lithium batteries are more advanced deep-cycle battery that also has zero maintenance.

  7. Can you run a deep cycle battery and a starting battery in parallel?

    It is not a good idea to connect a deep cycle battery with a starting battery in parallel as they have different charging properties. It will work but it will cause the life expectancy of both batteries to be reduced.

  8. Does an RV need a deep-cycle battery?

    Yes. An RV requires a deep cycle battery especially if it has appliances drawing power from the battery. A deep cycle battery will continue providing power constantly to those devices enough to run a 12v fridge, fan, and tv.

  9. Does a trolling motor need a deep-cycle battery?

    Yes, and here is why; when you are trolling a boat you are moving at a relatively slow speed, therefore, drawing amps from the battery slowly. A deep cycle battery is made for continuous use and depending on the size would last hours with this kind of use.

  10. How long do deep-cycle batteries last?

    A typical 12 Volt AGM battery will last around five years while a gel battery averages around four years. Premium deep-cycle batteries such as the Rolls-Surrette will average around 12 years.

    But this will depend on how these batteries are used, maintained, and recharged. Factors such as temperature, depth of discharge, and how many times the battery is being deep cycled also come to play. A battery discharged to 50% every day will last about twice as long as if it is 80% discharged.