can you put a deep cell battery in a car

[VonLucia]

Yes, you can physically install a deep-cycle battery in a car, but it is generally not recommended for standard daily driving. The primary reason is that deep-cycle batteries and starting, lighting, and ignition (SLI) batteries are engineered for fundamentally different tasks. An SLI battery, your typical car battery, is designed to deliver a very large burst of power—measured in Cold Cranking Amps (CCA)—for a few seconds to start the engine. A deep-cycle battery is built to provide a lower, steady amount of power over a much longer period and to be deeply discharged and recharged repeatedly, which is ideal for powering accessories in RVs or boats.

Using a deep-cycle battery in a car you start every day can lead to premature failure. The constant high-current draw from starting the engine can damage the thicker, softer lead plates inside a deep-cycle battery, which aren't designed for that kind of shock. You'll likely experience a much shorter battery life. The only scenario where it makes sense is in a specialized vehicle, like a dedicated off-roader with a winch or a car-show vehicle with a powerful sound system, where the battery is used primarily for accessories and you might have a separate, small battery just for starting.

Battery Type	Primary Function	Key Metric (Cold Cranking Amps - CCA)	Plate Design	Ideal For
SLI (Standard Car Battery)	Engine Starting	High (e.g., 600-800 CCA)	Thin, numerous plates	Daily driver vehicles
Deep-Cycle Battery	Sustained Power Delivery	Low to Moderate (e.g., 100-300 CCA)	Thick, solid plates	Trolling motors, RVs, solar storage
Dual-Purpose Battery	Combination of Both	Moderate (e.g., 400-550 CCA)	Hybrid design	Off-road vehicles, boats with single battery

For most people, a better alternative is a dual-purpose battery, which attempts to balance decent cranking power with a deeper cycle capability. It's a compromise that works well for vehicles that need to start an engine and also run accessories for extended periods.

[McDamian]

I tried it once in my old truck when my regular battery died and the deep-cycle was all I had. It worked to get me to the store, but it felt sluggish turning over. The guy at the auto parts store told me straight up: it'll wear out real fast if you use it every day. It's like using a long-distance runner for a sprint—they can do it, but it's not what they're built for and it'll beat them up over time. Just get the right battery for your car.

[Serenity]

Think about the purpose. Your car's main job is to start instantly, which requires a huge, brief jolt of power. A deep-cycle battery is built for endurance, like powering lights on a boat all night. Forcing it to be a starter battery stresses its internal components. You might get away with it temporarily, but you're sacrificing long-term reliability and potentially leaving yourself stranded. The chemistry and construction are optimized for different goals.