Batteries are expensive and keeping them in tip top condition means keeping them charged up and maintained. Batteries that are deeply discharged may never fully recover especially if they are of the conventional lead acid type, plates can actually buckle ruining the battery and in the cold winter months a 'flat' battery can actually freeze and the case can split dumping acid everywhere. Frankly until a few years ago the only charge my batteries got was from the engine alternator with the occasional top up from an automotive style battery charger on the odd time when I was tied up to a dock. The automotive battery chargers are cheap and they work sort of but they do not take into account the type of battery that they are being connected to, AGM, gel, lead acid and others all have differing needs as far as charging goes but the car style charger which is most probably of the resonant type puts out a high amperage charge which gradually tapers off as the battery is unable to accept higher charge rates. This all sounds fine and is often great for a quick top up but is not good for the battery which will often show charged when in fact it is not.
Boats and car batteries operate in completely different environments and I am not talking about one being on water and another on land. What you have to think about is that a car battery is pretty much being charged all the time that you are in the car. There are rare occasions when you may be sitting at the side of the road with the hazard flashers going but 99% of the time when you are sitting in the car the engine is running and thus the alternator is putting out a pretty hefty charge which could be of the order of up to 65 to 80 amps depending on your particular vehicle. Some of this current will go to charge the battery and keep in charged up and the residual current will be used to run the car electrics, ignition lights, radio etc etc. Modern car batteries are often quite small because basically all they have to do is start the car. If the battery is in good condition and the car starts readily any charge that is used up starting the motor is soon replenished and the battery is thus kept at full charge all the time. This is where the cheap battery chargers from NAPA or the auto parts store come in. If you inadvertently left your car lights on over night and the battery is flat all it often needs is a couple of hours with the clip on type charger and there will be sufficient charge to start the car whereupon the alternator takes over and after 40 minutes or so of driving the battery is once more charged up and will fully recover as the regular charging regimen with current from the alternator takes over.
Contrast this to the average boat. Typically even a modest boat may well have more than one battery which may be of different capacities perhaps a 80 amp hour for engine starting and 120 amp hour battery for house loads. The boat may often be left for weeks at a time and when it is used the engine may only be run for and hour or so and sometimes less particulary if it is a sail boat which is scant time to charge up even one battery let alone two. Then to add insult to injury the boat may be achored for a time while the crew fish or having cleared the harbor the sails are hoisted and the engine is turned off. Even with the engine off the radar and other electronics may be on which further depletes an already stressed battery. Even with a good 85 amp alternator on the boat the engine may ideally need to be run for several hours to fully charge the batteries but that does not often happen unless you happen to be on a power boat that is on a longish trip. Because the current decreases as the battery comes up to charge many boat batteries may only ever be 90 % charged at best all the time. The last 10% takes the longest to get into the battery.
The point of all this is that to maintain batteries properly they need to be fully and consistently charged. Many long distance sailors and liveaboards opt for wind generators and solar panels which are great for providing an almost constant source of power as long as the wind blows or the sun shines. For the rest of us however where the boat is tied up in a slip and there is a ready supply of shore power a marine style battery charger is the answer. One such charger is the ProMariner range of which I have been testing the 12 -20P model. Other models are available and which one you pick will depend to some extent on the size of the battery bank. Available from 10 to 60 amps in 12 volt and 20 and 30 amp models in 24 volt the 12 - 20 that I have been using is capable of charging up to three batteries with a maximum output of 20 amps which is more than enough to keep the two AGM batteries that I have on the boat fully charged. Designed to be permanently fitted into the boat the AC side operates on any voltage from 100 to 220 in either 60 or 50 cycles so it will operate in just about any area of the world without modification, a boon to world voyagers. Completely solid state it was easy to install and set up. The installation instructions are easy to follow and soft keys on the from panel allow you to set the charger to your specific requirements depending on the type of batteries that you have aboard. This is key as it means that the charging is specially matched to your batteries, thus output voltage is adjusted by the unit to give optimum charge irrespective of what type of batteries that you have. A temperature sensor connection also monitors the batteries reducing and adjusting the output depending on the battery temperature. Once the charger is set no further input is required from the boat owner and each time the power is connected the charger brings the batteries up to charge quickly, but just how quickly depends on how discharged they are. The big difference with this type of marine charger is that it is a three stage charger. Unlike the car charger that just reduces output as the battery voltage increases the ProMariner has three output phases; the bulk charge where a lot of amps are put into the battery quite quickly which may be up to the maximum of 20 amps, a float charge at a much lower amperage rate and finally a conditioning charge which may be a small percentage of an amp to keep the battery fully charged. Charging the battery like this is much better for them and after I connected up the charger for the first time I was surprised at just how much better my batteries performed, spinning the engine over noticeably faster. Prices vary depending on the model but the model I installed retails for around the $250 mark.
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