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Batteries: Lead Acid? The pro’s and con’s!

With the introduction of higher output alternators and electronic charge splitter systems on boats having vastly improved, to benefit fully from a decrease in recharge time and longer runtime, the correct battery choice should be made.  When making a battery purchase you need to consider – Battery life expectancy (how often is it to be used/number of cycles~), depth of discharge (how much power is required for each use?) and level of safety required (spillage and gas risk – Flooded Lead Acid compared to a Gel or AGM battery, for instance).

Lead-acid batteries come in several types, each with specific designs, advantages, and ideal use cases. Here’s an outline of the main types of lead-acid batteries:

1. Flooded Lead-Acid (FLA) Batteries (Not maintenance free)

1.1. Wet Cell (Conventional Flooded)

  • Description: Contains liquid electrolyte (sulfuric acid and water) that freely floods the plates.

  • Maintenance: Requires regular topping-up with distilled water.

  • Advantages:

    • Cheapest type

    • Long lifespan when well maintained

    • Good deep-cycle performance (in deep-cycle variants)

  • Disadvantages:

    • Requires ventilation

    • Risk of spills and acid leakage

    • Sensitive to vibration and orientation

1.2. Tubular Plate (Flooded)

  • Description: Uses tubular positive plates for enhanced durability.

  • Use Case: Industrial applications like forklifts, solar systems.

  • Advantages:

    • Longer cycle life than flat plate types

    • Better suited to deep cycling

  • Disadvantages:

    • Bulky

    • More expensive than standard flooded batteries

2. Sealed Lead-Acid (SLA) Batteries

Also called Valve-Regulated Lead-Acid (VRLA) batteries, these are sealed and maintenance-free.

2.1. Absorbent Glass Mat (AGM)

  • Description: Electrolyte is absorbed in fiberglass mats between the plates.

  • Advantages:

    • Maintenance-free

    • Spill-proof and vibration-resistant

    • Can be mounted in any orientation

    • Good cold-weather performance

  • Disadvantages:

    • More expensive than flooded types

    • Slightly less tolerant of overcharging

2.2. Gel Cell

  • Description: Electrolyte is mixed with silica to form a thick gel.

  • Advantages:

    • Excellent deep-cycle performance

    • Very low self-discharge rate

    • Works well in high temperatures

  • Disadvantages:

    • Very sensitive to overcharging

    • Lower power output (not ideal for high current draw)

3. Deep-Cycle Lead-Acid Batteries

  • Description: Designed for sustained energy draw and deep discharge.

  • Variants: Available in flooded, AGM, and gel types.

  • Use Cases: Marine, RV, off-grid solar, golf carts.

  • Key Features:

    • Thicker plates for deeper discharges

    • Longer cycle life under deep discharge conditions

4. Starting (Cranking) Lead-Acid Batteries

  • Description: Designed to deliver high current for short durations to start engines.

  • Variants: Available in flooded and AGM types.

  • Use Cases: Cars, trucks, boats, motorcycles.

  • Key Features:

    • Thin plates for maximum surface area

    • Not suitable for deep cycling

5. Dual-Purpose Lead-Acid Batteries

  • Description: A compromise between starting and deep-cycle batteries.

  • Use Cases: Boats with combined engine starting and house loads.

  • Advantages:

    • Can handle both starting surges and moderate cycling

    • Versatile for compact systems

Summary Table

Type Maintenance Cycle Life Deep Discharge Vibration Resistant Cost
Flooded (Wet Cell) High Moderate Good (deep-cycle models) Low Low
Tubular Flooded Medium High Excellent Low Moderate
AGM None High Good High Moderate
Gel None High Excellent High High
Starting (Cranking) Varies Low Poor Moderate Low
Dual-Purpose None/Low Moderate Moderate High Moderate

If you’re choosing a battery for a boat, AGM and gel types are often preferred due to their sealed, maintenance-free nature and resistance to movement and vibration.

For Lithium Batteries, please see the Technical Article: Batteries: Lithium? What’s the big deal?