I posted here about a year ago from Tahiti where I was attempting to assess whether or not my old wet cell house batteries were dying. Thanks to help from this board I was able to figure out that they were before my boat and I crossed to Hawaii. Luckily I was able to buy a new set of AGM batteries in Raiatea.
Now we are in Sitka, AK, and those AGMs are acting strange. I'm attempting to figure out if THEY are passing into the nether world.
During the passage here from Hawaii, I began getting unusual voltage readings. The batteries seemed to drain more fully than I was use to, but more worrisome, they began to take higher voltage charge before they were full. One factor may be that it got cold on this trip. From an average temp of 75-80*f in Hawaii down to 40*f mid high latitudes Pacific. I was also using some different equipment...a new chartplotter and radar...and my solar panels got less sun... I was forced to run the engine to charge every other day. While in Hawaii, the top voltage reading when batteries were full (using the engine's alternatore) was about 14.3v. Now to get the same charge amount, the final voltage reading is 14.6 or higher. At night the batts may go as low as 12.5 if used heavily where as expected tropical readings were 12.8 to 12.7. To me this sounds like they've lost capacity.
Today I performed a load test using a tester on loan from a local automotive store, the type that measures CCA and is rated up to 100amps. Beginning open cirquit voltage for each of the three batteries was 13.3. This was after charging them and letting them rest over an hour. I applied the load tester and flipped the switch and got very similar results for all three batteries. Each dropped quickly to a certain point and stayed. A) 11.8 volts; B) 11.6 volts; C) 11.7 volts. THE BIG QUESTION: Are these readings that suggest an AGM Battery is healthy? Certainly they would be for a deep cycle wet cell, but I don't know what voltage ranges to expect for AGM.
If they are healthy readings, then the only thing I can think is causing the wider range of voltage readings than what I was use to in Hawaii is the drop of 35 to 40 degrees in temperature. In your experience, is the above consistent with cold weather voltage readings for AGM batteries?
I have three 100 amphr AGM deep cycle batteries (group 31) made by YNC, Chinese and all that was available in Tahiti.
The side of the battery lists the following stats--
Constant Voltage Charge (really?--not usual for AGM)
Cycle Use: 14.5 to 14.9V
Standby Use: 13.6 to 13.8V
Initial Current: Less than 25amps
I don't know what "Cycle Use" or "Stansby Use" mean.
Thanks in advance,