With battery banks getting larger & larger and battery technology becoming more and more expensive a quality battery charger is not the place you want to skimp on features or quality.
For this article I am installing a Sterling Pro Charge Ultra. When selecting a marine battery charger there are certain things I find to be important.
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.
"WHAT WE FOUND
Ø Burnt and corroded shore power cords
Ø Improper AC Neutral to DC negative connections
Ø Reversed battery cables
Ø The failure of an automatic inverter ground switch
Ø Oversized breakers
Ø A BATTERY CHARGER INPUTTING 110AC INTO THE BATTERIES
Ø Wire nuts used
Ø Undersized wire
Ø Hard (house type) untinned wires"
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 battery temperature sensing and come with the sensor as standard equipment, not an "extra".
4- The charger needs to have a good warranty and the manufacturer should have a good reputation for customer service/support. This charger carries a 5 year warranty and the Support at Sterling Power USA has been outstanding.
5- The charger should include multiple options for charging voltages/programs.
6- The charger should be multi-stage with at least Bulk, Absorption, Float. I prefer them to also include a Conditioning/Equalizing program.
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 output a pure sine wave.
8-For charging wet cell batteries I prefer a charger that will revert to an absorption voltage periodically when left in standby/float mode. This programmed absorption voltage cycle helps to minimize electrolyte stratification. Float current alone is often not enough to prevent the electrolyte from stratifying. An absorption voltage, run periodically for a short duration, very often prevents the effects of stratification.
Stratification is when the acid sinks to the bottom of the battery case and the water rises to the top of the battery case. It creates uneven plate wear and can lead to premature death of the battery. A cyclic absorption voltage will get the electrolyte moving again and minimize any effects of stratification. Not all chargers offer this very useful "cyclic absorption" feature.