When selecting a marine battery charger, there are certain items that are important to look for:

1- The charger should be built to ABYC / UL 1236 standards. These standards are specific to the marine industry, though I think the emergency market such as rescue and ambulance also use UL 1236. This standard is created around safety and isolation of AC & DC. A UL 1236 charger has undergone a 1500 volt test to ensure there is adequate AC/DC isolation inside the charger. 1500 VOLTS !!!!! While there are some non-marine chargers that can do quite well in the marine environment the UL 1236 or “ABYC” compliant statement or logo will be a good guide and won’t leave you guessing if the charger you chose can handle the environment or is well suited to a marine application.

This quote was published in an ABYC referenced article and written by corrosion survey specialist Stanley Konz.

A BATTERY CHARGER INPUTTING 110AC INTO THE BATTERIES……OUCH!

It is critical you choose a well built charger and wire it properly. If you don’t fully understand the above points made by Mr. Konz you should consider consulting a qualified marine electrical systems specialist for this install.

That article goes onto say that nearly 1/3 of the boats in that marina were leaking AC current directly into the water! DIY wiring mistakes, even by those meaning well, can often be a major player in these “leaks”. Please be careful and follow acceptable safety guidelines.

2- The charger should work on varying input voltages and not suffer from output limiting. This Sterling PCU is a “World Voltage” power factor corrected charger and will work on any voltage from 90-260 volts/ 40-80 hz and still supply 100% of its rated output. You can plug this charger in to voltages in just about all countries on the planet. If you’re a cruiser this is a critically important feature. If you have a US voltage charger you’re stuck charging at US voltage/Hz docks.. There are MANY docks out there with voltage drop issues and even at 90 volts AC, with the Sterling PCU, you’re still getting the full rated charger output.

3- The charger should ideally offer physical on-battery temperature sensing, and should ideally come with the sensor as standard equipment, not as an “extra“.

4- The charger should have a good warranty and the manufacturer should have a good reputation for customer service/support. The Sterling charger I am installing for this article happens to carry a 5 year warranty, one of the longest in the industry, and the support from Sterling Power USA has been excellent.

5- The charger should include multiple options for charging voltages/charging profiles plus the ability to create a custom charging profile for batteries not in addressed by a preset list.

6- At a minimum the charger should be multi-stage with at least Bulk, Absorption & Float. I prefer them to also include a Conditioning/Equalizing option.

7- The charger should work well with marine generators. Many chargers, especially non-marine units, do not work well with a marine gen set as the generators do not always output a clean sine wave. The Sterling is PFC so it can handle a wide variety of inputs and tolerates generators that are slightly off spec rather well.

8- For charging wet cell batteries a charger that will revert to an absorption voltage periodically, when left in standby/float mode, is preferred over one that does not. This programmed re-absorption voltage cycle helps to minimize electrolyte stratification. Float voltage alone is not enough to prevent the electrolyte from stratifying. An absorption voltage, run periodically for a short duration, very often prevents the effects of stratification and re-mixes the electrolyte.

Still not understanding why? Okay…….

1- Car chargers, when used on boats, can be one of the worst offenders & cause of stray current corrosion due to their internal architecture which very often does not isolate AC & DC sides like a UL Marine charger will. So this = NO !!

2- Most of the car/auto type battery chargers use what is often referred to as an “autoformer” or autotransfomer. These are transformers with just one winding. Cheap, dirty and they can work ON LAND. Because of this single winding they share a common internally. Portions of the same winding act as both the primary and the secondary. This is bad news and not how a “marine” charger is built. With a marine charger all AC source current runs through the AC hot wire of the charger and is fully returned to shore via the white/neutral wire. The “case” is also grounded to the ships DC ground just in case it becomes energized in an internal fault. Again this = a big NO !!!! DO NOT USE AN AUTOMOTIVE CHARGE ON A BOAT……

3- If the “car charger” has a two prong plug, & many do, especially the older ones we all seem to have lying around the house, these can inadvertently become reversed. This is especially true if your boat has old AC outlets.. Follow me here, if the AC feed neutral & hot are reversed the ships DC negative bus can now become 120V AC with a “car charger”… This is what Mr. Konz observed in my statements in the last photo. You don’t want to be a swimmer near a boat with a cheap car charger on-board, trust me. You also do not want to be the cause of an Electric Shock Drowning or ESD.. So again this = a BIG NO!!!!!!!

But don’t just take our word for this here is Boat US one of the largest marine insurers in the United States: *Image Courtesy Boat US

This is a decision that is entirely up to the user, with some caveats. The general consensus, & industry recommendation, is to size a hard wired charger for a minimum of 10% of the banks rated Ah capacity, for flooded deep cycle batteries. A 400Ah battery bank, sized at 10%, would get a 40A charger. Sizing at 10% of Ah capacity of course assumes you have the time needed to charge at 10% of Ah capacity and no other loads while charging. Sizing on the larger side, for faster charging, should take into account the battery type you are charging eg: GEL, AGM or Flooded.

Pay Attention to Your Battery Manufacturers Suggested Charging Guidance!

When sizing a charger it is always important to pay attention to minimum charger sizing recommendations. Batteries such as Odyssey TPPL AGM’s, Northstar TPPL AGM’s & Firefly Carbon Foam all benefit from high current charging (40% of installed Ah capacity is advised). Lifeline AGM’s have a minimum recomendation of 20% of installed Ah capacity. This high current charging is beneficial to these batteries and leads to increased cycle-life. Ignoring minimum charging amperage guidance will mean that you’ll not get the optimum cycle life out of the bank.

The image below is for a single Group 31 Odyssey TPPL AGM battery. If you had four of these, for a 400Ah bank, you’d need 160A of charging to meet Odyssey’s “minimum” recommended charger guidance. The ProCharge Ultra can be run in parallel to achieve the minimum charge current guidance for batteries such as these. You can always choose to charge at a lower rate, but you are giving up cycle life by doing so.

The charger can always be larger and this will allow for faster charging.

If you choose to size on the low side, at 10% of Ah capacity, you should also consider any DC loads your boat will use while at the dock. You should always consider the DC dockside loads when trying to get to your minimum 10% sized charger.

For instance some power boats & sailboats have small banks, lets call it a 200Ah bank. A 200Ah house bank would suggest a 20A charger is necessary for a 10% of Ah capacity charge rate. However, what if your on-board loads are consuming 10A? When dockside, DC devices can consume power and rob it from what your charger can feed the bank. On-board items such as DC lighting, DC refrigeration, computers, TV’s stereo etc. are all taking charging potential away from the charger in order to run. Your dockside DC loads reduce the amount of current the charger can supply for battery charging. For example a 10A dock-side load, with a 20A charger, means that 10A is feeding your DC loads and the remaining 10A is going into the bank for charging.

A 20A charger with a 10A dockside load means the battery charger, sized at 10% of bank Ah capacity, is really only supplying 50% of its potential output for charging. This results in a charge rate of just 5% of of the banks Ah capacity. In this case you would need a 30A charger to maintain a charge rate of 10% of Ah capacity. As I said above, “with some caveats“.. Size carefully and don’t forget to consider the dockside DC consumption.

The Sterling Pro Charge Ultra battery chargers have no problem charging a large bank, even pretty small ones, and they can run at full output for many hours, but it does not mean they should. The concern is that all electronics have a shortened life when running hot for long periods of time. Sizing on the small side means a longer bulk charge duration (full charger output) and more heat to dissipate. For the longest duty cycle life a larger charger, that is in bulk for a shorter period, will last the longest. The cooling fan on the Sterling Pro Charge Ultra is a variable output design to let these chargers run quieter. Chargers with single speed fans are most often louder as the fan is either on or off. When sized trending towards larger the fans kick on very rarely but if you go small they work harder and the fan is in use more often.

Some chargers, usually fan-less units or “waterproof” units, can not charge large banks without suffering from damaging internal heat build up. This can result is a drastically shortened life for the charger especially if it is not sized tending towards the larger rather than smaller side. Some chargers reduce or throttle output when they get hot in an attempt to self protect. The more efficient the battery charger is, the less heat it will produce. The Power Factor Corrected Sterling Pro Charge Ultra is near 90% efficient. This is an improvement over non Power Factor Corrected chargers of as much as 40%. Still sizing a charger trending towards the larger side will mean less heat and a longer life.

What the heck does “Power Factor Corrected” mean? What it means is you’ll have a more efficient cooler running charger & less noise/fan run times. It also means a smaller lighter charger with a smaller foot print, because leas heat needs to be dissipated. You’ll also use less AC power to charge at the same DC output than a non Power Factor Corrected charger.

Even the Sterling ProCharge Ultra 60A model will easily run off a Honda EU2000i generator and leave you with plenty of left over wattage, about 700W left over, to run other devices while charging your bank at 60A. NOTE: The Honda EU2000i, a popular gas suitcase generator used on small boats, has a constant load rating of just 1600 watts and is not really a “2000 watt” generator for constant loads.

CAUTION: I DO NOT ENDORSE, CONDONE OR BELIEVE THE USE OF PORTABLE GAS GENERATORS, OF ANY TYPE, ON BOATS, IS SAFE.

I only made the statement above because I recognize there are a fair number of boaters out there who will still do this no matter how much you tell them it is an unwise and unsafe practice. There have been numerous CO poising deaths related to portable generator use on boats.. Be careful and please don’t become a future Darwin Award Winner.

If you had a 400Ah bank, and wanted it charged from 50% state of charge to full, over one day, you could get away with a 20A charger, but I don’t advise it. Of course just because you can charge a 400A bank with a 20A charger does not mean you should, as I have referenced above due to heat.

Conversely if you power your charger off a generator, when away from the dock, as many boaters do, you will want as much charger as your batteries will accept to keep generator run times as short as possible. My one and only real gripe with the Sterling chargers is the largest single charger is 60A. On vessels with large banks or AGM or other types of batteries that have high acceptance rates, a 60A charger can limit your recharge times when using a gen set to charge while away from the dock. For larger chargers Victron & Mastervolt make good ones, or you can simply double up on the Sterling Pro Charge Ultra’s. Using two separate chargers will give you the added benefit of a back up if the other charger fails. In bulk mode, which is what you’d be doing with genset charging, both chargers will be pumping out their maximum current to the bank and you’ll get through bulk pretty quickly. Need more current? You can go to three or more.

More often than not your battery charger will be located out of sight and the front control panel may not be easily accessible to see. To deal with this quirk many quality chargers offer a remote display panel. They are a good feature to look for when choosing a charger, if it can’t easily be seen.

The remote for the Sterling Pro Charge Ultra offers a multitude of display options including monitoring DC output voltage, AC input voltage, DC current output, battery temperature. charger temperature, transformer temperature, total charging time, charging time this event and just about anything the charger is doing or has done. It is one of the most informative remotes I have seen on a battery charger, at any price point.

Wiring the remote is simple, four mounting screws and two plug & play phone jack type connections. It can be flush mounted or surface mounted and both options are included with the remote, plus the cable.

Please be aware that any battery type or voltage programming for the PCU needs to be done via the front of the charger. The remote display is data only, it’s not designed for programming the charger.

Marine chargers from companies like Sterling, Mastervolt, Victron, ProMariner & others will often have a remote display option.

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If you are storing in a hot climate, above 75F then you really must leave the sensor connected. Heat is one of the major enemies of all batteries. If you have them in an engine room, which is not advised, or you live in a warm climate, you really do need a charger that features on-battery temperature compensation to reduce the charging voltage when the batteries begin to heat up. If your batteries can regularly exceed 80F then you’ll  need a charger with temperature compensation.

Earlier versions of temp compensation on some chargers was sporadically successful at best, bordering on dumb, as in not very smart. With newer technologies these sensors can be accurate to within a degree or two, which is more than enough.

Any charger that does not offer ON THE BATTERY temp sensing is simply not a smart charger.. Beware that many charges that claim “temp compensation” are doing this via ambient temperature at the charger itself. Ambient temperature sensing CAN NOT identify battery heating due to the effects of charging or discharging. If the charger is in a cool spot, and the battery bank is in an engine bay, you can literally cook your batteries. Ambient temperature sensing is NOT SMART…

Sadly the term smart charger is bandied about these days like a ping-pong ball. I think Deka / East Penn, one of the largest US battery manufacturers, cautions us very well on so called “smart chargers“.

Begin Quote:

Deka / East Penn Battery

“Unfortunately, many chargers on the market claim to be gel/VRLA “friendly” or “OK for sealed batteries”, but are not. Some overcharge the batteries, while others may not fully charge the batteries. Some chargers claim to be “smart”. Some “smart” chargers do a good job, others do not. The best choice of charger often depends on the application.

Almost all applications require temperature sensing and voltage compensation. Beware, many chargers measure the ambient temperature which could be significantly different from the battery’s internal temperature.”

End quote:

In this photo you can see how the charger is feeding the bank. With banks in parallel or series parallel it is important that the charger supplies it current across the bank. If you look you’ll see that the positive feed and the negative return pull off opposite sides of the battery bank.

Wiring this way forces the current to flow through the entire bank and helps to minimize any intra-bank imbalances. This is one of the most often violated rules of charging I witness on boats. It is important to note that this is not just for charging sources such as chargers, alternators, wind or solar but also for the DC loads. Always connect across your bank to keep intra-bank imbalances to a minimum. As banks get larger there are more precise ways of wiring that can lead to better balancing but doing it this was gets you a lot further ahead than pulling everything off one end.

You will also note the three bused ANL fuses on the left which protect the ALTERNATOR, HOUSE BANK and CHARGER wiring. The ABYC requires that any device connected directly to a battery be fused within 7″ of the + battery post to protect the wiring. These fuses are not intended to protect the devices but rather the wiring in the case of a dead short to ground. While the 7″ rule is often very tough to meet always try to get the fuses as close as you can to the battery + post. The wire marked HOUSE BANK + FEED is about 16″ long but runs in a conduit for about 9″, under the quarter berth, then comes out at the fuse.

Because the alternator and charger do not use the same size wiring as the house bank feed to the battery switch, they each need their own fuse to protect the wire.

When you parallel banks you add or combine the amperage as in Ah’s, cranking amps or short circuit amperage. These group 31 wet cell batteries can pump out in excess of 1200 cranking amps at 70F. For just two of these batteries that is 2400+ amps of cranking current at 70F.

The short circuit current is always multiples higher than the cranking amperage at 70F. Marine Cranking Amps (MCA) are rated at 32F and Cold Cranking Amps (CCA) are rated at 0F. As temps drop you have less available cranking ability and as the temp climbs the more cranking & short circuit ability you’ll have to fry things. 2400 amps is enough to weld metal with and that is not even the short circuit rating.

This is the fuse distribution bus discussed in the last photo.

The three ANL fuses are bused together with copper bar stock at the top of the fuses. The source wire from the house bank comes in the top and the ALTERNATOR, BATTERY SWITCH FEED, CHARGER/ACR are protected out the bottom.

There are many ways to fuse devices and banks like this. For this application I found the bused ANL fuses a good fit.

This photos shows the ANL fuses and buss bar. Just makes it easier to see.

One of the benefits of a charger like the Sterling is that you can use the charger as a 12V power supply if you disconnect or remove your batteries from the boat during off-season layup.

Wiring the charger direct to hard mounted buss bars and fuses, and not direct to the battery posts, means it can still power the vessels DC system even with the battery bank is disconnected and off line.

This illustration will better show how to connect charger sources and loads to your battery bank.

In most applications, it will be most optimal for battery balance, to connect across the bank. This will force the batteries to charge & discharge more evenly and uniformly and over the life will help to keep them in better balance.

I have used our shops battery testing equipment many times in scenarios like this, and in every example, I see the bank unevenly balanced. The batteries show these imbalances during testing. In a bank of batteries, wired like this, it does matter, over time. Don’t just connect your charge sources or loads to one end of a bank.
Of course you don’t need to take my word for it, this is what Odyssey Battery (EnerSys) has to say about properly connecting batteries in parallel:

The bottom negative wire on that buss bar is for the battery charger. If your boat is equipped with a battery monitor, the chargers DC negative wire must be placed on the load / DC system side of the shunt as is shown here.

In this photo I have plugged in the temp sensor and am testing the charger to see if it recognizes the temp sensor. It did.

With the Sterling Remote Panel the charger will tell you the battery, charger and transformer temp to within 1 degree. A pretty cool feature.

The AC wiring should be sized based on the manual for your charger. For this charger it calls for 14/3 AWG AC colored wire. The input for the AC wiring is marked L – N – G or BLACK/HOT, NEUTRAL/WHITE & GREEN/EARTHING GROUND.

Your charger should ideally have it’s own dedicated breaker in the AC panel sized to protect the AC wire you’re using. It is not suggested to share a breaker with any other device for a fixed mounted charger. This one uses a 15A breaker and 14/3 AWG AC color coded wire.

Always install your AC & DC wiring to acceptable color code standards. For AC and a single phase charger like this it is:

Green = GROUNDING/EARTH

Green = BONDING or EARTHING

In this picture I have mounted the charger to a back board which will get mounted to the boat.

The wires are affixed to the board with sufficient strain relief to prevent inadvertent loading of the attachment point to the charger. The ends of the wires are crimped with ring terminals using the proper tool and then sealed with adhesive lined heat shrink. I also coat the lugs with a terminal grease to prevent oxidation/corrosion at the lug/terminal strip interface.

One of the more critical aspects of charger installations, that I nearly always see violated, is the green case ground wire shown. If I had to guess I would say that nearly 85% of the installations I see are either not case grounded or the case ground wire is to small.

This green grounding wire grounds the chargers metal frame to the vessel and allows your over current protection devices to work properly, if there is an internal fault that shorts to the case.

A fault in the DC side can supply enough current to overwhelm and overheat the AC green grounding wire. It can even do this well before tripping a fuse or breaker. It is a must do requirement that the case be bonded/grounded/Earthed with a green wire of not less than one size smaller than the DC conductors!!

This green wire gets sized for the DC side of the charger. The green AC ground will not satisfy the ABYC case ground requirement on an AC/DC battery charger. Follow me on this one. If there is a fault on the DC side of the charger the AC green wires size may not be able to handle this fault and could be undersized in having to handle that fault. This is why the requirement for the chargers case ground is for no less than one size smaller than the DC output wires.

The ABYC standard suggests that the case ground for chargers needs to be no less than one AWG gauge size smaller than the DC output wires. So, if you have 6 GA DC wire then you need no less than an 8 GA case ground wire. Even if your wire is already technically “over sized” your surveyor or insurance company may not know this so it is always best to wire it equal to or no less than one AWG size less than the DC output wires.

It is always a good idea to check with your battery manufacturer and obtain the recommended ABSORPTION, FLOAT and EQUALIZATION voltages.

You will then program your charger to your batteries using the preset charge algorithms. Some chargers offer very little in the way of “smart” charge programs, sometimes four or less, and others, like this Sterling, offer plenty of options. As mentioned the Sterling PCU chargers also offer a user defined program that you can self program. Very cool for those applications that need it.

You can always choose to use GEL or AGM settings on wet cell batteries but a good quality charger will not go into equalization mode, and should not, while in AGM or GEL mode. If charging WET batteries with a GEL or AGM program you’d need to switch back to a WET program to equalize your batteries. In contrast you should NOT use AGM or WET settings on GEL batteries.

What Are BC Mode and PS Mode?

A number of years ago the State of California mandated that battery chargers were no longer allowed to float charge batteries. Once charged the charger needs to stop charging or even floating the batteries and go into a sleep mode. The Sterling ProCharge Ultra ships in BC mode (BC = Battery Charger). When California mandated this, the ProCharge Ultra’s original BC mode became the new CEC (California Energy Commission) compliant mode.  For owners who do not want to use the charger as a CEC compliant charger, this can be easily changed by selecting PS mode during the chargers boot-up period.

There is some confusion on the net regarding exactly what PS mode (PS = Power Supply) actually does. Some folks incorrectly assume PS mode is a constant float and lacks bulk the absorption stages. PS mode is not a constant float and it will do BULK, ABSORPTION & FLOAT. What it will not do is go to sleep, after float, as California would prefer.

The video below should help to clear up any confusion on this subject.

Sulfation is like cancer of the battery, once it has set in it is only a matter if time before the battery passes on to battery heaven. Equalization is like chemotherapy. It helps prolong the life but only prolongs the inevitable for some time. Please do not over equalize your batteries as it can cause plate decay and lead to shorter life if over-done. On the flip side don’t be affraid to equalize when signs are present that you need to. The best thing you can do for your batteries is keep them at or near 100% state of charge as often as possible using the highest safe absorption voltages allowed by your battery manufacturer. If you’re on a mooring this will require wind or solar, an alternator simply won’t do this, and the batteries will sulfate prematurely.

I much prefer to equalize batteries one at a time and monitor the progress with a hydrometer or, what I use, a sight refractometer. A good charger with temp sensor should monitor the temp but it never hurts to have a digital infrared thermometer on hand while equalizing. Please DO NOT equalize batteries unattended! It is very wise to be there during equalization. If you are unfamiliar with equalization PLEASE research this before hitting the button. To equalize one at a time simply disconnect the batteries not being equalized.

Thoroughly test your charger before leaving it to do it’s thing. I personally don’t like “unattended” charging even with the best built chargers in the world. This is just MY personal preference, so consider it, but don’t take it as gospel. For unattended charging I use solar. It works for us, but may not for you.

Unfortunately for many boaters in warmer climates, with WET cell batteries, the ambient temps require that chargers be left on and most often “unattended”. This is due to the exacerbation of battery self discharge in warmer temperatures. Heat kills batteries, cold helps prolong life.

Sulfation and self discharge greatly accelerate the warmer battery temps are, so do keep your batteries topped up as often as you can. In a perfect world all chargers would perform flawlessly for 20+ years. Sadly for the boating public we don’t live in a perfect world and many a charger has taken out a perfectly good bank when it decided to pack it in, we see it far too often. When owners leave a charger on constantly, while the vessel is unattended, a charger failure can go unnoticed until it is too late. It can sometimes take the batteries out with it. A simple unattended charger failure now becomes an entire new bank and a new charger as opposed to just a charger. If you don’t need your charger on constantly, consider not leaving it on while it’s unattended. Balancing unattended charging & its potentials for failure modes, versus the potential for self discharge and the resulting sulfation is one you’ll have to tackle on your own.