Marine Accessories

Tired of Replacing Batteries Every Two Years?
A better Understanding of Batteries Will Help Resolve Your Problems
by David Pascoe

One of the most common problems I run into on surveys is dead or severely depleted  batteries. The usual reason why boat batteries are dead is due to having the wrong type, size or quality to meet the vessel’s demands. Truly good batteries are expensive and there are few boat builders that provide good batteries with new vessels; usually the quality is minimal, the amount of power inadequate, and the type ill-suited. The subject of batteries can be rather complex, but I’m sure most boat owners would rather not know too much about the details of how batteries work (or fail to work). The discussion of batteries can be divided into two major topics, battery construction and application, and charging. This essay deals mainly with battery construction and application, and will help you gain a better understanding of what type is best for your application, as well as what is needed to maintain them for longest service life and reliability. Application means the type of boat you have, how it is used, and the kinds of equipment on it.

Until the recent advent of electronic chargers we had big problems with ferroresonant chargers overcharging and damaging batteries. Now, to the best of my knowledge, all electronic chargers provide the basic 3 stage charging with electronic sensing that prevents overcharging. Therefore, if you have an old charger and are having premature battery failure problems, you’d best replace the unit. Symptoms of overcharging are hot batteries and unusual fluid loss.
System Designs
Batteries lie at the heart of all pleasurecraft DC electrical systems but there is wide variation on how DC systems are set up, meaning what purpose is assigned to each bank. The vast majority of all boats have relatively simple 12 volt systems consisting of banks of one, two or four batteries connected in parallel. Larger yachts may have 24 or 32 volt systems. In the standard, or I should say typical marine system, each bank is used for starting one engine, but is also wired to a battery selector switch. The selector switch may have positions marked 1, 2 or ALL. Other switches are marked ON/OFF, in which case bank source cannot be changed. In most cases the selector switch controls which bank runs the house system. In older boats, engine starting may be controlled by the switch. The ABYC standard requires all boats to have a master shut off switch, but not a selector switch.
Battery parallel switches join two batteries together in parallel (doubles amperage, not voltage), even if both are low, will often start an engine that won’t start on one bank alone. This facilitates the starting circuit alone and will have no effect on the house system.
Boats which have a selector switch are usually set up in such a way that the source for the house system can be selected via the switch. In many, if not most, later model boats the house system is permanently wired to both banks. With older and particularly larger boats, there is likely to be one bank dedicated as the house bank.
Generators should have a separate starting battery so that if the main banks go dead, the generator can still be started. This is not always the case.

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Unfortunately, batteries are made in so many configurations and types that there are no quick and easy answers for those that desire quick answers. This essay is the culmination of several weeks worth of research into battery fundamentals, standards and testing. It is not a technical treatise of scientific exactitude because were I do so, this essay would end up dozens of pages long and I’m sure you have no interest in reading that.
This essay is intended to be of most benefit to those of you who suffer from the problems of premature battery failure and all-to-frequent replacement. If you’re ever wondered why there is so much conflicting information about batteries, it is because not many people bother to take the time to learn, including many people that sell batteries. Amongst experts, there is wide agreement about performance of various types because actual performance is easily proven.
Contrary to popular misconception, the so-called “maintenance-free” battery is anything but. The only difference between the this type and those not so designated is that you don’t have to top off  the electrolyte (add water) when it evaporates,  but batteries still need to be maintained in other ways as they will not function properly when ignored. Sealed batteries are not really sealed because all wet cell batteries have to be vented in order to discharge the build up of pressure during charging. Thus, even maintenance-free batteries can loose fluid, especially as a result of over charging. The primary difference is that one cannot add water to a “sealed” battery, though some will leak if laid over.
These batteries are also not maintenance free because they will naturally discharge themselves over time at a rate of anywhere from 1% to 15% per month, depending on type. These batteries should not be left uncharged month after month, but should be maintenance charged on a regular basis. Total discharge will destroy a battery so that it will never take a full charge again.

Most inboard powered boats are fitted with shore power systems and battery chargers to keep the batteries charged. Up until recently all battery chargers were the ferroresonant type capable of “trickle” charging, that is, supplying a very low charge rate sufficient to keep the batteries up to snuff. The problem with those older chargers was that they had a bad tendency to overcharge and boil all the electrolyte away which damages and eventually ruins the battery. Overcharging is deadly to gel cells.

The introduction of electronic, 3-stage chargers in recent years has been a vast improvement in battery maintenance because these chargers are able to sense when the battery cannot take any more charge and then shut off.

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