Re: Batteries what kind?
I think this is a defnitive article about the subject which comes from West Marine. It is the appraoch I use.<br /><br />
<br /><br />ntroduction <br />"Any boat that relies on its engine(s) for propulsion and travels more than a short distance from shore should have two independent batteries capable of starting the engine(s)." That kind of platitude is so darned obvious, you probably wonder why we'd waste your time with it. But the fact is, the statement is insufficient and misleading. This West Advisor will try to explain why. <br /><br />Due to the scarcity of tow trucks at sea, boaters have to be more self-sufficient than their land-bound counterparts in RVs and automobiles. Judging from the statistics we see on boat breakdowns, the two most frequent requests for assistance are because, 1) "I'm out of gas!", and 2) "I can't crank my engine. " We'd also venture to guess that the reason most boaters can't crank their engines is because their batteries have been run down by too much use and too little charging, as opposed to starter motor failure or some other malady.<br /><br />Assuming the boat is equipped with two adequate batteries, why would they both end up dead at the same time? There are at least three probable causes:<br /><br />Poor battery charging by the engine. This may be masked by near-continual battery charging, via shore power, when the boat is not in use. <br /><br />Inadequate battery capacity, forcing the boater to use both batteries simultaneously (switch on the BOTH position) to run DC loads. <br /><br />Lack of true isolation of the engine starting bank and the house bank, resulting in unintentional simultaneous discharge. <br /><br />The latter reason is the least understood by boaters, and it's due to a simple myth: because my boat has a big red OFF-1-BOTH-2 battery switch, it therefore has isolation between its battery banks. To that, we say:<br /><br />Nonsense!<br />Most single-engine boats produced in the last thirty years are supplied with two nearly identical (and under-sized) marine batteries. Generally of the Group 27 designation, both batteries could be used interchangeably for starting and house loads. Prior to starting the engine, the operator would turn the battery switch to the BOTH position so that he or she had the full cranking power of the batteries. Once the engine started, the operator would leave the switch in the BOTH position while powering to the day's destination so that both batteries were charged. Once a sailboat began sailing sans engine, or a powerboat dropped the hook, the operator would (in theory) turn the battery switch to the 1 or 2 position, so that the other battery would be reserved for starting. When it was time to crank the engine again, the battery switch would be turned to BOTH, or possibly to the reserved battery, and the engine would be started. <br /><br />The problem, of course, is that this requires a lot of thought on the part of the operator, who is trying to relax in the first place. The inevitable result is that at some point, the boater accidentally leaves the battery switch in the BOTH position, resulting in two very dead batteries.<br /><br />We also take issue with using two identical batteries since boats have two distinct types of loads: long duration, low amperage loads when the engine (charging source) isn't running, and high amperage, short duration loads while starting. Using a pair of deep-cycle or dual-purpose batteries, or worse yet, starting batteries, for this application is inefficient.<br /><br />What's the solution?<br />We strongly recommend that you select and wire your batteries differently from the way the factory wired them. Use a stout starting battery to crank your engine, based on your engine's cranking requirements. Use a larger house battery with triple the capacity of your daily DC requirements. Now this is where it gets complicated: we DON'T recommend the use of a traditional OFF-1-BOTH-2 battery switch. Instead, consider using three OFF-ON battery switches as follows: one switch to connect your starting battery to your starter circuit; one switch to connect your house battery to your boat's distribution panel; and one switch to parallel your battery systems if either battery fails. <br /><br />With this switch set-up, you simply turn your engine and house switches to the ON position whenever you are onboard, whether anchored, starting your engine, or sailing. The battery parallel switch remains OFF unless there is a complete failure of either battery bank or you have run your starting battery down trying to crank a reluctant engine. When your engine is off, the starting battery is safely isolated from the house loads. It cannot be discharged, even if you leave your stereo on all night, listening to Jimmy Buffett and blending margaritas. <br /><br />How do I charge both banks simultaneously?<br />By isolating starting and house banks, you face a challenge trying to charge them from a single source like single-output chargers or alternators. If you violate the "separation" of the two banks, you face the probability of two dead batteries due to "operator brain-fade". That's why we are great believers in the West Marine Battery Combiner and Heart Pathmaker, Balmar Dual Output Alternators, and to a lesser degree, battery isolators. These products sense the voltage of the battery banks and connect the batteries together whenever one battery's voltage is elevated. Both banks charge simultaneously and remain combined until the voltage drops, whereupon they are disconnected from one another. It's much like having a very attentive engineer flip your battery parallel switch on and off at exactly the right moment. The result is maximum charging performance for two banks, and complete isolation of the two banks to ensure that you can start your engine. <br /><br />Do I have to scrap my present switch?<br />While you don't have to, we strongly recommend the use of simple-to-understand OFF-ON switches. Shoot, even your brother-in-law can probably figure out how to operate an OFF-ON switch, but might be completely baffled by a OFF-1-BOTH-2 switch. Alternatively, you can use your current battery switch, plus a second OFF-ON switch, but we think it becomes complicated to understand what each switch combination accomplishes. As an added benefit, the fact that the battery switches are seldom, if ever, operated while underway greatly reduces the chances of damaging your alternator by accidentally opening its output circuit.
