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Deep Cycle vs Starting Batteries in Diesel Applications
Diesel engines require high torque and strong bursts of current to crank, especially in cold weather or under load. Traditionally, starting batteries—also known as cranking batteries—are used for this purpose. These batteries are designed to deliver a short, high-amperage surge to turn over the engine. In contrast, deep cycle batteries are built to provide steady power over long periods and withstand repeated discharge and recharge cycles. Their internal construction features thicker plates and denser active material, which improves longevity but reduces peak current output.
Terminology Clarification
Operators have experimented with deep cycle batteries in diesel machines ranging from skid steers to farm tractors. While some report successful starts in warm climates or with smaller engines, others encounter sluggish cranking, voltage dropouts, and premature battery failure. One technician in Alberta noted that his 4D31-powered loader started fine with a deep cycle battery in summer but struggled below freezing. After switching to a Group 31 starting battery with 950 CCA, the issue disappeared.
In emergency situations, deep cycle batteries can start a diesel engine—but they are not ideal for repeated use. The high current draw during cranking stresses the plates, leading to sulfation and reduced lifespan. Some users have tried pairing two deep cycle batteries in parallel to increase available amperage, but this adds complexity and still may not match the performance of a dedicated starting battery.
Recommendations for Diesel Equipment Owners
While deep cycle batteries can start diesel engines under certain conditions, they are not engineered for high-current cranking and may fail prematurely when used this way. For reliable performance, especially in cold climates or with high-compression engines, a dedicated starting battery with sufficient CCA is the better choice. Hybrid solutions like dual-purpose batteries offer flexibility but should be matched carefully to the machine’s demands.
Diesel engines require high torque and strong bursts of current to crank, especially in cold weather or under load. Traditionally, starting batteries—also known as cranking batteries—are used for this purpose. These batteries are designed to deliver a short, high-amperage surge to turn over the engine. In contrast, deep cycle batteries are built to provide steady power over long periods and withstand repeated discharge and recharge cycles. Their internal construction features thicker plates and denser active material, which improves longevity but reduces peak current output.
Terminology Clarification
- Cold Cranking Amps (CCA): The amount of current a battery can deliver at 0°F for 30 seconds while maintaining at least 7.2 volts. Diesel engines typically require 800–1,200 CCA.
- Reserve Capacity (RC): The number of minutes a battery can supply 25 amps before dropping below 10.5 volts.
- Dual-Purpose Battery: A hybrid design that offers moderate cranking power and deep cycle durability, often used in marine or RV setups.
Operators have experimented with deep cycle batteries in diesel machines ranging from skid steers to farm tractors. While some report successful starts in warm climates or with smaller engines, others encounter sluggish cranking, voltage dropouts, and premature battery failure. One technician in Alberta noted that his 4D31-powered loader started fine with a deep cycle battery in summer but struggled below freezing. After switching to a Group 31 starting battery with 950 CCA, the issue disappeared.
In emergency situations, deep cycle batteries can start a diesel engine—but they are not ideal for repeated use. The high current draw during cranking stresses the plates, leading to sulfation and reduced lifespan. Some users have tried pairing two deep cycle batteries in parallel to increase available amperage, but this adds complexity and still may not match the performance of a dedicated starting battery.
Recommendations for Diesel Equipment Owners
- Use batteries with at least 800 CCA for engines under 4 liters, and 1,000+ CCA for larger displacement or turbocharged diesels.
- Avoid using deep cycle batteries as primary starters unless the engine is small and ambient temperatures are mild.
- Consider AGM (Absorbent Glass Mat) or EFB (Enhanced Flooded Battery) designs for better vibration resistance and cold performance.
- For dual-use scenarios (e.g., powering accessories and starting), opt for dual-purpose batteries rated for both CCA and deep cycle endurance.
- Compact diesel engines (e.g., Kubota, Yanmar): Dual-purpose battery with 600–800 CCA may suffice.
- Mid-size tractors and loaders: Starting battery with 950–1,200 CCA recommended.
- Heavy equipment (e.g., excavators, dozers): Group 31 or larger starting battery with 1,200+ CCA essential.
While deep cycle batteries can start diesel engines under certain conditions, they are not engineered for high-current cranking and may fail prematurely when used this way. For reliable performance, especially in cold climates or with high-compression engines, a dedicated starting battery with sufficient CCA is the better choice. Hybrid solutions like dual-purpose batteries offer flexibility but should be matched carefully to the machine’s demands.
