All,
Puzzling, at least to me, I have very low battery bank 1 readings after one night a mooring.
I have 2 4D AGM batteries (just over 2 years old) conservatively rated to provide 400ah, which to my understanding results in approx. 200 usable amp hours to maintain bank 1 at a level of 50% discharge.
Last night, I had the fridge and anchor light on overnight and used approx. 40 amps according to my Cruz Pro DC Monitor
At 8AM in the morning, the bank 1 voltage reading was in the 11.9 range, and readings fluctuated up and down, back to the 12.5 – 12.6 range.
Attempted to start the boat on bank 1 to no avail, but my one AGM Bank 2 battery fired up the engine with an initial voltage read of 13.19.
This situation has occurred 3 or 4 times since May 15th.
Couple of questions?
Should the bank 1 voltage display correlate with the amp hours used on the DC monitor? If I have only used 50 amp hours overnight, which represents 25% of my total available AH, should I not have a bank 1 voltage reading around 12.5 or higher?
Can I continue to use all of my 200 amp hours without over discharging the bank 1 batteries?
A battery trouble shooting sites states “when voltage quickly drops to 11V or less when using power, this usually means the battery has a faulty cell and needs replacement”.
On the other side of the coin, our marina technician tested bank 1 and found batteries to be OK. He states after anchoring overnight, the batteries will normally read lower voltages, unless allowed to rest with no load.
Any insights into my situation would be appreciated.
Bill & Barb
s/v Northern Lights
2002 Catalina 36 MKII #2086
Rock Hall, MD
Northern Chesapeake
I have two Catalina's one. 36 & second a 380. Many years ago I put a 160 amp alternator on both boats with surpentine belts. Also carry a starter battery on both boats that I never use but it is their. i do not have any solar panels except for a small one on my 36 in Punta Gorda. i also have Boat command on both boats so i can keep track of the Florida boat when I am up in NY on the 380. The only problem I have had over the years is that my ac battery charger started to go after ten years so I flew home to Punta Gorda and put a new one in. We try to change everyday when on anchor especially during the epidemic. Hopefully this gives you another approach to the same problem we all have. Charging our batteries. We are in NY for the summer on our 380 but we also have two houses one in Florida and one in NY.
c36 MKII 1996 #1523
North Star M35
Punta Gorda Fl - Hurricane Ivan
stephenemmerman.blogspot.com
The tech is correct. Using the voltage if a load is/was recently present will misrepresent the state of charge. A fully charge AGM should be 13 volts. At 12.1 volts 50%, but that is only true if no load has been present for 24 hours. The fact that you can't start the engine on the house bank is an issue, however. First, when you get on the boat disconnect shore power and check voltage after a few minutes. My guess is 40 amps is a good measurement for the amount of energy you used at night with the fridge and an anchor light. If your voltage reads 12.5 you probably have a bad cell. Before using your two year old batteries as an anchor, clean all the terminals. It is amazing how little corrosion effects charging capacity.