In the market for a new marine battery? Give Century Batteries a call on 0800 93 93 93.
Coastguard members get a special trade discount on batteries nationally.
Batteries generally fall into two parts: either starter batteries, or deep cycle batteries.
Starter batteries can be considered the 'sprinter' - they give lots of power quickly, but not for long. Their capacity is described in Cold Cranking Amps*, a measure of how much starting power it has on a cold morning.
Technically, it's the number of amps a regular 12v battery can deliver for 30 seconds at below freezing temperature (-18 degC/0 degF), without dropping below 7.2v. The higher the CCA number, the better.
Starter batteries should never be run below 80% of their capacity.
*Some batteries might be measured in Marine Cranking Amps - it's the same measure as CCA, except measured at a warmer temperature (0 degC/32 degF). Because batteries perform better in warm (but not hot) temperatures, the MCA number is often 20-25% higher. Don't confuse the two though - remember to compare like-for-like!
Deep cycle batteries are the marathon runner of the battery world. They can deliver a good amount of power consistently, for long periods. They're usually measured in Amp-hours (Ah), and a good rule of thumb is to not discharge them below 50% of their capacity.
Marine batteries are built tougher, to suit the slamming around boats can take. They generally have much higher capacities than car batteries, with a higher reserve capacity to run on-board gear.
Most modern marine batteries are maintenance free, meaning they're completely sealed and you don't ordinarily need to top them up with distilled water.