Why can't I use any old marine battery?

Today's fuel injected motors with their computer control modules and high energy ignition systems place a high demand on the battery. Every engine manufacturer will provide you with the correct battery rating information for each model. Take for example you have a 2005 Yamaha 225 HP four stroke, the service manual list the minimum recommended battery capacity as: CCA-512 A, MCA-675 A, RC-182 Minutes.

Now to break that down a little further, the CCA stands for cold cranking amps (the amount of amps the battery  can deliver at 0°F  for 30 seconds without going below 10.5 volts), MCA stands for marine cranking amps (the amount of amps the battery  can deliver at 32°F  for 30 seconds without going below 10.5 volts), and RC stands for reserve capacity (this is the time in minutes the battery can deliver 25 amps @ 80° F without dropping below 10.5 volts). The reserve capicity is important because if the alternator fails, this will determin how long the engine will continue to run so you can get back to shore. 

Make sure to check your engine specifications before replacing the battery.  Also, make sure to use properly torqued hex nuts with lock washers not the wing nuts that often come with marine batteries.