Deep Cycle Batteries Explained

WHAT IS A DEEP CYCLE BATTERY?
A deep cycle battery is a lead-acid battery designed to be regularly discharged then recharged again. In a battery, one discharge plus one recharge equals one cycle.

WHAT IS THE DIFFERENCE BETWEEN DEEP CYCLE AND STARTING BATTERIES?
• Deep cycle batteries (marathon runners) are designed to deliver sustained power with low current draw over extended periods of time
• Starting batteries (sprinters) are specially designed to start the engine, work as a voltage stabiliser and run accessories when the engine is not running

GRID DIFFERENCES BETWEEN DEEP CYCLE AND STARTING BATTERIES
Deep cycle batteries have thicker plates to handle deeper discharges, different grid patterns to improve current flow, higher density paste to increase cycle life and use different grid compositions depending on battery type (AGM, flooded or gel) to maximise service life.

WHAT IS DEPTH OF DISCHARGE (DOD)?
DOD is the amount of energy that has been removed from the battery, which is expressed as a percentage of the total capacity of the battery. For example, 50% DOD means that half of the energy in the battery has been used. 80% DOD means that 80% of the energy has been discharged so the battery now holds only 20% of its full capacity.

BATTERY TIP 1 - Select a deep cycle battery that suits the environment!
When choosing a deep cycle battery, many consumers focus on the price, physical size, weight or capacity of the product, without taking into consideration where the battery is located in the application.
• Near sensitive electronics - use a Yuasa AGM or SMF flooded battery. Avoid using maintainable batteries as the higher gassing rates can corrode and damage the electrics in the application.
• In confined spaces - use a Yuasa AGM or SMF flooded battery. Avoid using maintainable batteries as they can be difficult to check the fluid levels and may fail prematurely due to lack of maintenance.
• Under seats and sleeping areas - use a Yuasa AGM or SMF flooded battery. Hydrogen and oxygen gas produced from maintainable batteries can be damaging to your lungs and respiratory system when inhaled.
• When fitted under the bonnet - use a Yuasa maintainable/SMF flooded battery.

BATTERY TIP 2 - Regularly check the state of charge in your battery!
When the battery is not in use, recharge it if the open circuit voltage (OCV) drops below 12.5 volts. Deep cycle batteries are not designed to be kept in a low state of charge and will build up sulphation on the battery plates that will reduce the performance and cycle life of the battery.

BATTERY TIP 3 - Do not overfill maintainable deep cycle batteries!
If you have a maintainable battery, it’s important to check if the battery has sufficient electrolyte covering the battery plates. If topping up is required, do not over fill when the battery is discharged as the fluid levels will rise when the battery is charged and may overflow. Top up using distilled or demineralised water and never fill with sulphuric acid. When the battery is fully charged, fill to the bottom of the spout extensions.

BATTERY TIP 4 - Never fully discharge a deep cycle lead acid battery!
The deeper you discharge the battery the more it will reduce the battery’s total cycle life. We recommend discharging a battery to no lower than 50% DOD, with a maximum of 80%. If you discharge the battery to 50% of its capacity instead of 100%, the battery will produce an extra 40% more amperes over the life of the battery.

BATTERY TIP 5 - Always ensure the charging settings match the battery!

Charging Current (Amps)
Recommended charging parameters for lead acid battery types:
• Flooded batteries: 10% of the battery’s Ah rating (100ah = 10 amp charging current)
• AGM & Gel batteries: 20% of the battery’s Ah rating (100ah = 20 amp charging current)

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Do you know the main reason lead-acid batteries break down and lose capacity? Battery sulfation. It’s the cause of these issues 80% of the time. But with the right tools for battery maintenance and a little investment of time, you’ll bring your batteries back to life and keep them functioning reliably. Learn everything you need to know about battery maintenance.

Batteries are poorly understood, even by that living off-grid that depend on them for power. A better understanding of the inner-workings would go a long way in keeping those batteries happy. Given how expensive batteries are, and how they are a major (recurring) expensive of an overall off-grid system, battery care should be high on everyone’s off-grid list.

Starter batteries, semi-traction batteries, traction batteries, and even stationary batteries all need maintenance to perform to their full potential. Regularly perform the six essential maintenance tasks we outline here to optimize the performance and reliability of your lead-acid batteries.

Regular Inspection and Maintenance

Regular testing and inspection will help to maximize battery life. A routine inspection at least once a month is recommended to maintain optimum performance.

Add distilled water to the lead-acid battery

The fluid in your lead-acid battery is called electrolyte. It’s actually a mixture of sulphuric acid and water. When your battery charges, the electrolyte heats up and some of the water evaporates. During a process called electrolysis, the water breaks down into hydrogen and oxygen gases that dissipate. The result? The electrolyte level in the battery lowers over time.

If the electrolyte level is too low, the plates in the battery cells are exposed and will suffer damage. In addition, the sulphuric acid will be more concentrated. This means you need to replace the electrolyte. This is how you do it.

1. Check the battery water level with a level indicator

How do you know when to add water to your battery? It’s one of the most common questions we are asked. You could constantly check your battery or every battery in every machine in your fleet, but this is horribly time-consuming and there are easier approaches. Indicators are specifically designed to check the battery water level for you. They notify you whenever your battery needs to be topped up.

There are different systems available. One of these is the Smartblinky. You mount it behind the battery plug. Does it have a green light? Your electrolyte level is fine. When the light turns red, you know it’s time to add water to the battery cells.

Do you add water to your battery before or after charging? Always make sure the electrolyte covers the battery plates before you charge. If the plates are covered, charge the battery and then top up as necessary. This is because the electrolyte will expand during charging and is more likely to overflow if you’ve already topped it up before charging.

 2. Make sure you always have distilled water nearby

Never fill a battery with normal water. It will damage your battery. You need to use distilled water. It’s also known as deionized water and demineralized water. Basically, it’s water that has been filtered to remove metals and minerals that may interfere with the processes in your battery.

Buy distilled water from a hardware store or automotive parts specialist. It’s also easy to make yourself. You need simple tap water and a demineralization device like the Hydropure. The simplest of these devices are filled with a type of resin. You let the tap water flow in, the resin filters the metals and minerals out of the water and you’re left with the deionized, demineralized, distilled water that’s suitable for use with your battery.

 3. Install an automatic battery water filler system

How much-distilled water do you add to your battery? That’s another question we are often asked. The answer varies from one battery to the next. This is one reason why we recommend using a battery water filler system.

A battery water filler system uses filler caps with floats that are connected to each other via water hoses. They keep your battery from over-filling. And they save you time. All you do is run distilled water into the hose. The filling system does the rest.

Battery Charging

Charging a lead-acid battery is the process of replacing the energy removed during discharge, plus EXTRA to compensate for any charging inefficiencies. The amount of energy necessary for complete recharge depends on the depth of discharge, rate of recharge and temperature. Typically 110% - 150% of the discharged ampere-hours depending on battery type must be returned to the battery to achieve full recharge.

Safety First

Before attempting to charge a battery with an external battery charger, it is important to be aware of the safety precautions when charging batteries and follow the instructions outlined by the charger manufacturer.

● Turn the charger off before attaching, rocking or removing the terminal clamps.

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● Keep open flames and sparks away from the battery.

● Keep vent caps in place.

● Charge in a well-ventilated area.

● Follow the battery charger manufacturer’s instructions to avoid overheating.

Dangerous explosive gases are generated during the charging process that can be ignited by a variety of sources including, sparks, naked flames, and static electricity. It is highly recommended to wear PPE (Personal Protection Equipment) including safety glasses, chemical resistant gloves, and overalls.

Selecting the Correct Charger

Lead-acid batteries should be charged in 3 stages; constant current (boost), constant voltage (absorption) and float charge.

When choosing a battery charger, it is important to select a charger that delivers the specified charging voltage and current to suit the battery type. Flooded, Absorbed Glass Mat (AGM) and Gel battery types require different charging specifications to provide optimum performance and service life. 

Charging Voltage (for manual chargers)

Monitoring battery voltage during charging is extremely important to reduce the risk of overcharging and to check the progress of the battery during recharge. Always keep inside the parameters outlined in the below table. Failure to do so can result in permanent damage to the battery.

Auxiliary Charge Voltage by Battery Type

Type Absorption Charging Float Charging Flooded (Maintainable / SMF) 14.4 to 14.8V 13.2 to 13.5V* AGM (Absorbed Glass Mat) 14.6 to 14.8V 13.6 to 13.8V Gel Electrolyte 14.2 to 14.4V 13.6 to 13.8V

The recommended temperature during charging is 25°C. Charging must be paused if the battery reaches 50°C.

The above specifications are for 12-volt lead-acid batteries. When charging 6-volt batteries, half the voltage specifications provided.

In addition to following the battery charging voltage guidelines, selecting the correct charging current (Amps) for the battery size is crucial to provide performance and service life.

Charging Current (for manual chargers)

Factors Affecting Battery Life

As batteries age, they gradually lose their capacity as their function is performed. The constant charge and discharge eventually lead to failure. Components corrode over time, electrical shorts occur and vibration causes damage; all eventually causing failure. Overcharging and undercharging of a battery will also have a bearing on battery life.
 
Battery Inspection

Check electrolyte level - fluid below the tops of the separators indicates overcharging or poor maintenance. The overcharge condition may be due to incorrect voltage setting, low voltage caused by heat or internal defects, or old age deterioration.
 
● Is there electrolyte on the top of the battery? This can indicate overcharging or overfilling.

● Is the battery loose in the carrier? This can cause failure from vibration.

● Does the battery have signs of damage or mistreatment? This can also cause failure.

● Discharged (flat) Batteries

A flat battery should be checked with a hydrometer. A low Specific Gravity reading of 1.220 or less in all cells indicates a discharged battery and it must be charged before further examination and testing can occur. The discharged condition may be due to a problem in the electrical system (slipping alternator belt, faulty regulator or alternator, high resistance due to corrosion). Internal shorts may also be due to manufacturing defects or shorts through the aging process or vibration damage.
 
Early Warning Signs

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