Charger separated for AGM

[KARL]

Hello, I have a 2015 RT27 classic with 4 AGM Group 31 batteries. One is a cranking battery for starting and the others are deep cycle, one for the Thrusters/anchor windlass and the other 2 for the house bank. When I am using the Promariner charger with shore power, set on the AGM setting, is my boat wired to separate the batteries charging? In other words, if the start battery is fully charged it can be overcharged and damaged while charging the other batteries. I'm not gettng the life span on them that I thought I would. Hope you can shed some light on this. Thank you.

 

[Rode Trip]

Your charger is probably the ProMariner 12-20P model. It is a 3 bank charger. It can charge house, thruster, and start batteries independently. It won't overcharge them as long as the setting on the front is set to 'AGM'. It will go through 3 steps, Bulk, absorption, and float with it safely holding them all on a float charge once fully charged which won't damage the batteries.

 

[KARL]

Yes, it is a Promariner 12- 20P. Thank you for the response. It is set on the AGM setting. Good to know they are being charged properly.

 

[BB marine]

You will not get the life expectation that you would expect with the standard Ranger Tug installation. For one reason the standard 20 amp Promariner charger is not nearly large enough for a battery bank as large as yours. Four batteries at a rated 100AH per battery is 400AH of battery. AGM batteries have a lower resistance than a standard LA flooded this allows them to be charged faster without the fear of excessive heat. It is better for an AGM to charge at a higher amp charge while in Bulk. The minimum charger I would use in a four battery bank AGM would be 40 amp and prefer to be 60 amp. The engine battery is not usually in need of charge like the house bank is and the thruster battery depending on how much you use it is not either. The problem with the Ranger install is the three bank charger that puts out in your case 20 amps is charging the batteries all at the same rate basically as if the charger is a single bank charger. Why? Because the way Fluid motion wired it. There are ACR's used to isolate the engine battery, house battery and thruster battery. When there is no charge and battery voltages are at 12.7 Volt +/- .3V all batteries are independent. When the charger is on and the battery voltage of any of the batteries reaches 13V for 90 seconds or 13.6 for 30 seconds the ACR joins the batteries as if they are wired in parallel. Now all batteries charging as one battery. If all batteries are in like kind and all batteries are of the same age and AH this is ok. The charger needs to be large enough to maintain the bank. 20 Amps IMO is not. If one battery is older and has a higher internal resistance than the other ones this is not the best way to maintain longevity of the newer batteries. If one battery has a weak cell it will eventually damage the other batteries by over charging the batteries. AGM are expensive batteries and one would expect to get twice the use out of them when compared to cheaper Flooded LA batteries. In my experience that is not the case with an installation like what you have. I had the same in my Cutwater and did not experience longevity out of AGM batteries. I used the boat and anchored a lot and used battery. The 20 amp charger was not big enough and the battery configuration worked but it is not the best.

The way a Ranger is set up I would purchase Flooded LA batteries and plan on replacing them every 3 years. Leave the install as is. Many have used it this way with no issue. I know how you used your boat in the past. The same way I did in My Cutwater. The AGM did not give me good service. I had the same set up as you. I switched to LA Flooded and got the same service life if not better than I did the AGM. When I sold my Mainship Pilot last fall it had the same batteries that I installed in August of 2021 Group 31 Flooded La. Inexpensive Duracell (East Penn) 105AH batteries. I had spent 14 months living on board while doing the Loop and 3 more months the following year cruising the Great Lakes anchoring and using battery all the time. The LA Flooded still tested with a low internal resistance and maintained a good full charge after four years of full service. I did have a 40 amp charger and a 50 amp solar Charger which helped.