Unik Techno • September 8, 2020

What are the physical differences between a lead-acid car battery and a lead-acid deep-cycle battery?

The physical differences in the external construction is generally wrt the take off terminals.

A car battery classified as automotive battery invariably has taper terminals with positive terminals being of a bigger diameter compared to negative terminals which are of a relatively smaller diameter. These are of a defined standard size conforming to international standards and SAE specifications.


Deep cycle batteries have taper terminals or L shaped terminals or embedded type terminals such that the customer can connect lugs of cable using different types of terminations.

The physical differences in the internal construction is as follows:

Automotive batteries have very thin positive and negative plates with number of plates being more so that the surface area is very high to enable delivery of high currents required for engine cranking applications.


On a like to like same Voltage & Ah basis deep cycle batteries have thick negative plates and much thicker positive plates if the batteries are of pasted plate type. In case they are of tubular type the positive plates are of heavy tubular design construction types and negatives are made of thick pasted plates. The number of plates per cell is also lesser in relation to automotive batteries.

The separators used in automotive batteries are very thin with low electrical resistance and the separators have a lower back web thickness.

The separators used in deep cycle batteries are much thicker with thicker backwebs to resist the effects of oxidation during cycling.


The lead busbars used for connecting the plates together in parallel and lead components for interconnection of cells as well as pillars on the end terminal sides are much thicker in deep cycle batteries compared to automotive. This is required since voltage drops are not acceptable when connected to a continuous load during long duration operation of the deep cycle batteries.

The vent plugs of a deep cycle battery are of the Flip Top type to enable water topping up which is required more frequently in the case of deep cycle batteries. Deep cycle batteries are subjected to 80% depth of discharge on a daily basis followed by a recharge daily thereby requiring water top up more frequently.


In certain cases the vent plugs of deep cycle battery are designed to be compatible to the auto filling system unlike in automotive batteries. Automotive batteries are nowadays fitted mostly with coin flush vent plugs which need not be opened for upto six months at a stretch.

The weight of automotive batteries are much lower compared to a deep cycle battery of same voltage and Ah capacity.



I have restricted my answer to the physical differences externally visible and to the physical differences of components which are obvious during manufacturing process.


By Unik Techno August 1, 2025
Sulfation is a widespread yet often overlooked issue in the world of lead-acid batteries. Frequently dubbed the “ silent killer” , it operates without obvious warning signs, quietly reducing both battery performance and service life. Whether used in industrial machinery, UPS systems, or off-grid energy storage, sulfation poses a serious risk to any application reliant on reliable battery power. What is Sulfation in Lead Acid Batteries? At its core, sulfation refers to the accumulation of lead sulphate crystals on the battery’s internal plates. This occurs naturally during discharge as the active material on the plates reacts with sulphuric acid. In a properly maintained battery, these crystals dissolve again during the charging process. However, when a battery is left undercharged, stored in a discharged state, or routinely subjected to deep discharge cycles, these sulphate crystals begin to harden. Over time, they become dense and irreversible, severely inhibiting the battery’s ability to hold and deliver electrical charge. What Causes Sulfation in Lead Acid Batteries? Understanding the root causes of battery sulfation is the first step to avoiding it. One of the most common contributors is infrequent or incomplete charging. A battery that is not brought back to a full state of charge after use may retain a residue of sulphate on the plates. This residue becomes the starting point for permanent sulfation, especially if the battery is neglected over repeated cycles. It is not just charging habits either—environmental conditions also play a significant role. High ambient temperatures accelerate the electrochemical reactions inside a battery, increasing the likelihood of crystal formation and growth. In warmer climates, or in confined battery enclosures without proper ventilation, this risk is amplified. Prevention of Sulfation in Lead Acid Batteries Prevention begins with proper charging practices. Always use a smart charger that can automatically adjust the charging voltage and current based on the battery’s state-of-charge. These chargers typically include bulk, absorption, and float stages that ensure a complete and balanced charge. Some models even include pulse or maintenance modes that help dissolve early-stage sulphate deposits, reducing the onset of crystallisation. Routine maintenance is another critical factor. For flooded lead-acid batteries, it’s important to regularly check electrolyte levels and top up with demineralised water when necessary. Low electrolyte levels expose the upper portions of the battery plates to air, causing oxidation and increasing the likelihood of sulphate build-up. In addition to fluid checks, make sure to clean terminal posts, check for corrosion, and tighten connections to ensure efficient current flow. Equalisation charging is a powerful tool in the prevention arsenal. This is a controlled overcharge applied periodically—usually once every 30 to 90 days that helps equalise the voltage between cells and reverses mild sulfation. Equalisation charges are particularly effective in larger battery banks where cell imbalance is common. However, they should only be performed according to the manufacturer’s guidelines, as excessive overcharging can damage the battery. Storage practices also matter. If a battery is left unused for extended periods, it must be stored fully charged and kept in a cool, dry environment. Batteries in storage should be recharged every 60 to 90 days to prevent the slow self-discharge that can lead to sulphate crystallisation. Even sealed lead-acid batteries are vulnerable if stored improperly. While some specialised de-sulfation chargers claim to reverse sulfation through high-frequency pulse technology, their effectiveness is generally limited to early-stage sulphate deposits. Once the crystals become hard and dense, recovery is unlikely, and battery capacity is permanently reduced. Prevention remains far more effective than any attempted cure. The consequences of ignoring sulfation can be expensive. Reduced runtime, increased charging times, and eventual failure can disrupt operations and require premature battery replacement. For businesses, this translates to higher operational costs, increased downtime, and reduced energy efficiency. At UNIK Batteries, we believe that prevention is the smartest investment. By manufacturing high-quality lead-acid batteries and state-of-the-art charging components, we help customers protect their power infrastructure from day one. Whether you operate forklifts , golf carts , maintain a solar backup system , or manage a unit of UPS batteries , we have the right solution to keep you powered and protected from sulfation. Contact us to explore our range of batteries and charging components today!
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