Types of 12V Lead-Acid Batteries for RV Use

First off, what’s this lead-acid stuff?

Batteries for automotive, marine, and RV use use internal lead plates and the action of sulfuric acid to generate electricity, which gives the name lead-acid.

Think of a battery as holding a certain amount of electricity. A lead-acid battery is rechargeable, which means it is constructed so that it can discharge electricity during use, and can then be recharged to its former level or amount of electricity. Proper discharging and charging helps extend the life of the battery.

Lead-acid batteries are designed to produce a specific voltage of 6V or 12V. Think of the voltage (the unit is the Volt, symbol V) as being like pressure from a garden hose. 12V is twice the pressure of 6V. Amperage (Ampere or Amp, symbol A) is the rate of flow of electricity. Think of 10A as being a gusher and 0.1A as a trickle.

Types of Lead-Acid Batteries

According to Interstate Battery Systems International, lead acid batteries can be basically grouped into two types

  1. Deep cycle batteries are engineered to be capable of being deeply discharged hundreds of times. A deep discharge is is defined by Interstate as one which drops the charge by 40% or more. For a 12V battery, this means a drop to 7.2V or less.
  2. Automotive starting batteries (also called Starting/Lighting/Ignition or SLI batteries) are designed specifically to provide a short burst of high-amp energy and to do this thousands of times over the product lifetime. They may be able to deeply discharge only a few dozen times before damage results.

Both types of batteries must be appropriately recharged after each use. A discharge and subsequent recharge is called a cycle. A deep-cycle battery is engineered to endure repeated deep discharges and recharges. A starting battery is built to endure repeated intense shallow cycles.

Flooded Lead Acid vs Sealed Lead Acid Batteries

Marine/RV lead-acid deep-cycle and starting batteries come in two different types: flooded (FLA) and sealed (SLA)

Flooded or liquid-electrolyte batteries

  • Contain free liquid sulfuric acid solution.
  • Have vent caps to allow gas discharge (gasses formed from evaporation and during charging are vented into the atmosphere)
  • Can spill acid if tipped or shaken
  • Tend to corrode around the electrodes
  • Require regular inspection and maintenance
  • Require care for safe transportation and storage

Maintenance of a FLA battery includes cleaning corroded electrode posts, checking electrolyte levels, and adding distilled water when necessary to top up. Car motor starting batteries can be the liquid electrolyte type because they are usually easily accessible for servicing.

Sealed lead acid (SLA) batteries

  • Do not expel external gases (the gases are recombined internally)
  • Do not leak
  • Do not require maintenance or inspection

The reduction in maintenance makes SLA batteries attractive to many consumers. And for some RVs a sealed starting battery may be preferred if it is in a difficult location.

Choosing Starting or Deep Cycle Batteries

Starting and deep-cycle batteries are available in similar sizes and with similar performance ratings; it is the intended use that determines which type is best. When the need is for a brief, intense discharge (such as cranking a car starter motor or running a discharge pump), a starting battery is best. For a long, slow and steady discharge (such as running low-amperage appliances, lighting etc.), a deep-cycle battery is the choice.

As for liquid versus sealed lead-acid batteries, the choice is clear. The reduced maintenance and reduction of potential for corrosive acid spills make SLA batteries the recommended product for use where the battery or battery bank is not easily accessible (such as tucked away in a cubbyhole in the RV coach).