I have read a ton of misinformation on the differences in optima batteries and was confused myself so here yall go, straight from optima:
What is the difference between RedTop, YellowTop and BlueTop batteries?
RedTop: Use this for normal engine starting where an alternator immediately monitors the state of charge and provides energy to the battery whenever it is needed. This would describe most stock vehicles.
* Automotive and RV under-hood starting
* Heavy equipment where starting is the primary function
* Diesel powered vehicles with no aftermarket electronics
YellowTop: Use this when electrical loads are higher than average, or when the discharge cycle is more than typical engine starting, such as vehicles without alternators. This also includes vehicles with significant electrical loads that may exceed the average alternator output (for example aftermarket audio system, GPS, chargers, winch, snowplow, inverters, drag cars). This can also include vehicles that have a lot of electronics from the factory, such as a minivan with power sliding doors and a DVD player, especially if the DVD player is used when the engine isn’t running.
* Racing vehicles without a charging system (alternator or generator)
* Dedicated drag racing vehicles
* Diesel powered vehicles with aftermarket electronics
* Car audio/video applications exceeding 250 watts over the OE system
* Vehicles or heavy equipment with inverters, hydraulics, winches or other accessories
* Electric vehicles
BlueTop: The BlueTop starting battery (dark gray case) is to be used when a dedicated starting battery is required and it should never be used for cycling duty. The dual purpose BlueTop (light gray case) can be used for both starting and deep cycling; it is a true deep cycle battery with extremely high cranking power.
* Trolling motors, marine applications with heavy electrical accessories and RVs should use a dual purpose BlueTop (which is both a starting and deep cycle battery)
* Use a BlueTop starting battery for marine applications and RVs when the battery’s only function is engine starting
Note: The difference between BlueTop and YellowTop deep cycle batteries is that BlueTop batteries have both automotive (SAE) posts and threaded posts, while YellowTops (other than D31T) only have SAE posts.
If you ever get confused on the color tops just remember: if it has a dark gray case then it is a starting battery; if it has a light gray case then it is a deep cycle (dual purpose) battery.
Optima Battery FAQ - Frequently Asked Questions
Hope this helps to clear everyone up!