Batteries and Battery Chargers For The Boat

The charging system on Beach House is coming along and is a major improvement from what we started with. It is also a bit unconventional for a boat charging system. After many years of installing these systems on my own and other boats I am always looking for a better and simpler way. The trend on boats today is to move away from simple into the complex as manufacturers try to integrate more systems and get single pieces of equipment to do more. The results have been more breakdowns and fewer repairs that can be done by owners. More capabilities and information are at your fingertips, but at a cost. In the last year, I have heard more and more reports about the Iota battery chargers and their use on boats. These units are not just chargers but converters as well. This means that the 12 volt system on the boat can be run off these units even if a battery were not connected. Not all marine battery chargers can do this and some can be damaged trying. The units convert the 120 volt AC to 13.6 volts nominal DC. The units are called "smart chargers" because they will deliver maximum current for whatever period of time needed to replace the charge but not stress the batteries. It will cut back to virtually milliamps once full charging has been achieved while still maintaining the proper voltage and will maintain that voltage under whatever demands are placed on it. The units are completely silent and do not run hot like many other chargers. They also use what Iota calls Tight Line Regulation which insures that the output voltage stays steady from no load to full load. This will keeps onboard pumps, lights, and motors operating at the correct voltage and thereby increasing their life. An equalization charge on the batteries on a regular basis goes a long way to prolonging the batteries life. The Iota will sense if an equalization charge has not been done for a week and will equalize without overcharging and gassing the water out of the batteries.

There is one drawback to these units. They are not designed for multiple banks of batteries. For that reason I had put off installing one until I did a bit more research and determine how others have overcome this shortfall. In discussion with other boat owners and the helpful folks at Iota the answer for us was simple. The chargers range from 15 amp up to 90 amp. The solution to our dilemma turned out to be as simple as installing a charger for each battery bank. By installing two chargers, which can be done in series or parallel , you have doubled what a single charger will do. By installing a single 45 amp charger on each bank we can charge them most efficiently and will have a back up in the event one would fail. A bonus is that even with two chargers they are less expensive than most of the "marine" chargers on the market. But we still had one more problem to overcome. With the starting battery we actually have three banks to charge.

Once again the solution was simple with a little research. Many of the expensive charger/inverter units have a built in Echo Charger specifically to charge the start batteries. These Echo Chargers can be bought separately and are perfect, in my opinion for starting batteries. The starting battery really only needs to be charged for a short time after the engine is started. The alternator usually does a quick job of this and after that a maintenance charge is all that is needed. A dedicated charger for the start battery would seem to be a waste of energy. The Echo charger can be connected to the starting battery via the house bank and the chargers can maintain any amps removed from the house bank by the Echo Charger to maintain the starting battery. This can allow all charging systems, the battery charger and the alternator, to be connected to the house bank where charging is needed the most. For the time being the alternator is connected to the battery switch which allows us to choose either bank or both to be charged off of the alternator. I am not happy with this set up since I would prefer to have the alternator connected to the house banks so perhaps a relay will solve that part, but that has not been done yet.

This set up may not work for every situation but we have found it perfect for our current charging needs. The house bank consists of two sets of two 6 volt deep cycles at 220 amp hours each for a total of 440 amp hours. These are equivalent to two 8D's which would cost four times as much and weigh four times as much. In the past we have averaged about 6 to 7 years for each pair with this set up and 8D's over the years have not given us better service. The start battery is a single heavy duty truck battery for cranking. When we are cruising our power demands are rather high so an efficient and simple charging system is important to us.


  1. Hi Chuck
    Let me make sure I have this right. Currently we have a single 8d house we will have to work with it for the time being since it is only 2 years old. We have a series 31 starting battery. We have a seperate 24 series battery for our little old 3kw onan..which runs like a watch.
    I have a xantrex 1500 watt inverter/charger. Currently we have a battery switch. The 31 series in on position 1 on the switch and the 8d is on position 2. The inverter charger is wired directly to the 8d and the echo charger on the inverter is wired to the small 24 series onan battery. The 31 series is not being fed by a charger at all. The alternator is connected to the switch.
    Would you suggest a different configuration? Perhaps the alternator hooked up directly to the 8d? Add an echo charger for the 31 series? Would like your opinion. Hope the weather has been better for you...has been around 100 degrees in our area last week...but getting better now. Are you using a genset on your boat? Keep up the great posts.
    George and Donna
    email the looks of the Iota 45.

  2. George, I am not sure which battery charger you have and if it will handle single or two battery banks. You don't say how the charger is connected to the system. I guess I am confused since you say the 31 is on the switch so the alternator is in fact charging it when the engine is running and the echo charger is charging the 24 if I understand correctly. Your set up is far from ideal and not how I would do it but it depends on how much you want to change the system. But the charger is the unknown so I can't answer all of your questions. A good battery combiner to charge your starting batteries from the charger or the alternator would be the best way to go IMO for your current set up. Chuck

  3. Hi Chuck,
    Your website is awesome. I am in the process of installing pretty much exactly the same battery system as this in my 1975 CHB, a sister ship to your boat. I was wondering if you did the work yourself or if you hired it done. I'm interested to know what size wire you used for the series/parallel connections at the batteries, and what size wire you ran to the switch from there. Is 1/0 enough at the batteries, would you know? Is 14 ga enough for the run to the switch? What would you recommend for a new battery switch? I have the original switch on the original panel, which is the same panel you have.
    Thank you for your time.

  4. Denise, 1/0 is fine for the batteries. 14 gage will never work for the run to the switch. The size depends on the run from the batteries to the switch, to the panel and back to the batteries. We put a wire size chart on the posting for installing the windlass that should be able to help you. The switch on the panel should be fine as long as it is still in good condition and no corrosion but if you need to replace it go with a Blue Seas and a minimum of the 300 amp switch. I have done all of the work on the boat myself, but I have been a service technician in the marine industry for over 30 years. I would recommend that you get Nigel Calders book on boat electrical and maintenance. It will be a great help in almost every project you will be working on. We used 1/0 wire from the battery bank to the battery switch and also to the panel. I like to oversize this particular run. The same for the ground. Good luck and I hope this helps. I do recommend with any electrical work on a boat that if you are not sure waht you need to do, get professional help. A poor installation can lead to serious problems. Chuck


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