Car and Truck Batteries are not the same. So not only are they different but they shouldn’t be used interchangeably. Duh! That should be obvious, right?
You likely already understand the differences in these two types of batteries if you own or have been around a RV (recreational vehicle) or boat. Deep cycle batteries are also found in golf carts and larger solar power systems (if you haven’t dealt with solar power yet, during the day the sun produces power that is captured & stored in these types of batteries so that at night items that need power can get it from the batteries that were “charged” during the day).
There is one more sometimes unknown use for deep cycle batteries. This use is as an alternative type of generator during an emergency. Instead of gasoline powered generators, deep cycle batteries are “inverted” and used to power the items that would’ve been powered by the gasoline generator.
There is something that deep cycle and car batteries do have in common though – they are both lead-acid batteries, so the same chemistry is used in each to produce energy. The difference is in how they are optimized to operate.
The design for a car battery is for it to give the cars engine a large amount of power, enough to turn over & crank, within a very short time period. In essence, just for the amount of time that it takes for the engine to turn over & start. The alternator / generator then work in tandem to kick in & start charging the battery instead of discharging it any more.
It is important to note that the car battery is not expected to drain completely during its life. In fact that is a bad thing if it does.
In normal operations the car battery may never discharge more than 20% of its capacity. In order to work this way, the cars battery is designed with thin plates so that its overall surface area is increased.
To contrast now, a deep cycle battery is able to provide a consistent, steady level of power for a longer period of time. It is capable of providing a surge of power but the amount of power available during the surge is significantly less than the car battery. Like its name suggests a deep charge battery will be deeply discharged. That is to say, that it is expected that the deep cycle battery will be deeply discharged constantly over its life. So, maybe as expected the deep cycle battery has very thick plates.
Rating types are essentially the same for car & deep cycle batteries. That is to say, the terms are the same (CCA & RC) but the values assigned to each in their specs are different. The deep cycle has 2-3 times the RC & delivers 1/2 to 3/4 of the CCA.
A deep cycle will experience several hundred complete discharges over its life while a car battery isn’t intended to be discharged completely.
CCA = Cold Cranking Amps
RC = Reserve Capacity