Question: The photo I sent in shows one of the batteries on my boat, an Optima brand marine trolling battery. It seems to work just great and I really haven’t had any problems with it. I am thinking of adding an additional battery to give me more capacity and am a bit confused. When I go to the Optima Batteries website, I see yellow, blue, and red batteries shown.

Optima trolling battery

I really don’t understand all the technical information the battery people give us so I’m just not sure which of the three colors to choose. Except for the color, they all look the same. Help!

Answer: Good question. Don’t be embarrassed by not understanding all the numbers and jargon that describes new batteries. It is confusing, for sure.

Essentially batteries today get thrown into three very general use categories -- starting or cranking for getting your engine started, deep cycle, which is what your trolling battery is designed for, and a comparatively new category simply called as “combination,” which is really a general-use compromise solution.

In the case of the Optima brand, they are further characterized by the fact that they are “AGM” technology, or absorbed glass mat construction, which means that the electrolyte solution inside the battery is immobilized by the mat material squeezed in between the plates in the battery. There is certainly much more going on inside these batteries in terms of tech, but we just don’t have space here to get into all of that detail. Essentially with the Optima, the red series batteries are clearly designated as engine starting batteries only. Simply, this means that they are engineered to provide a comparatively high amount of amperage for a brief period of time, long enough to get your engine(s) started.

The Optima blue and yellow series are a bit more complicated to differentiate from one another. Basically the blue series is loosely designated for marine use, but you need to be careful because the blue series offers both engine starting and dual-purpose configurations. The Optima 34M model, for example, is intended for engine-starting use only. All of the other models in the blue series are intended for dual use applications, both engine starting and deep-cycle use.  When comparing the yellow vs. blue series, it’s hard to determine any real difference. Comparing the specifications for a blue series BCI group 31 size to a yellow series BCI group 31 size shows that the only physical difference between the two is the stud size at the terminal connection point. The blue series uses a 5/16” stud and the yellow series uses a 3/8” stud. Aside from that I see no difference except a $10 variation in list price, the yellow series being slightly more expensive.

When all is said and done, the key specifications to focus on besides voltage are power ratings in either CCA (cold cranking amps) or MCA (marine cranking amps). These numbers must at least match your engine manufacturer’s minimum requirements. Also, on the deep-cycle side of things, the reserve capacity of the batteries in minutes is important. The higher the reserve capacity, the more deep cycle capability implied. This will vary depending upon how much DC load you apply, and for how long. The basic specification for determining reserve capacity is how long the battery in question can be subjected to a 25-amp rate of discharge at 80 degrees F before reaching a 10.5-volt cut-off point. It seems to me that either the blue or yellow series can work in marine applications based on Optima’s own specifications.