Charging / Discharging issue



I agree with everyone else's and your assessment that something is not right.  Get yourself an inexpensive Battery Tester like this one:

It's not a "real" load tester that a professional marine electrician would use.  However, I have one and was able to compare it's results side-by-side with a real load tester when I purchased my new batteries last year.  The results were very close (within 5% or less) to the "real" load test results.  Certainly close enough to see if one or more of your batteries has an issue and is compromising your whole battery bank.  I would get one of these ASAP and test each battery.

Also, you really can't trust the "% of Charge" on your battery monitor for much.  Here is a very long and detailed article as to why:

SM #440 Cara
Deale, MD USA 

John Clark

Agree with Ryan and Kent, something is not right.  I have six 110Ah AGMs and run the galley frig, one salon freezer, a 24v portable chest cooler, VHF, anchor light, and a 230v inverter supplying an icemaker, and two laptops and phone chargers. There is an occasional load from the microwave.
  We have 630 W solar which carries the constant load, and charges batteries at ~5 amps during a sunny day.  In the evening the battery will discharge at a rate between 2 and 10 amps depending on what is cycling on.  Average night we will draw down the battery ~24%. 
  My routine is to run the genset once in the morning and bring the batteries to ~95% then let the solar complete the charge during the day.  The charge starts out putting in ~95A and tapers down as the battery voltage comes up. Charge time is usually an hour or less. 

Like you we run 100 amps of charging via one 60A and one 40A charger which work together until voltage reaches 28 volts.    Our finishing voltage is 28.5V.  The chargers float the battery at 26.5V, the solar floats at 27.5V   We have a battery monitor on the DC breaker panel in the galley that monitors charge rate, Ah in/out, voltage and % capacity.  

The % capacity is a "calculated data point."  It uses some information that you have to program in including the size of the battery bank.  If the size is incorrect it will affect how it calculates capacity.  

I don't think your genset would affect the charge rate or battery issues, so you can at least not worry about that part of the system. 

A photo of your battery monitor and maybe take some readings of voltage, current and %capacity every 15 minutes during your next charge would help figure out what is going on. 

            Regards,  John

SV Annie, SM 37
Druif Bay, Water Island USVI

---In amelyachtowners@..., <ryan.d.meador@...> wrote :

Hi Olaf,

How were you measuring the battery capacity?  Are you using a built-in battery monitor?  I wonder if there could be something wrong with that.  What did it show for the charge current when you were running the 100A charger?  What about the charge current when the solar and wind were going?  What was the current draw from your electronics?

Are you sure all of the batteries are connected?  Check the connections, and also check any battery terminal fuses that may be installed.

It would be worth a sanity check with a multimeter to verify the voltage at the battery bank is what the monitor claims (and you can also use this voltage with some tables you'll find online to estimate the state of charge, if there is no load/charger on the bank when you took the measurement).  You can also use your multimeter to measure the voltage across the shunt resistor used by the battery monitor; with the shunt's resistance (should be printed on it) and Ohm's law you can verify the current flow.

SM 233 Iteration
Boston, MA, USA

On Sun, May 6, 2018 at 10:59 PM, Kent Robertson karkauai@... [amelyachtowners] <amelyachtowners@...> wrote:

You definitely have a problem, Olaf.  I have 90AHr batteries, and they last 10-12 hrs at anchor, an hour or so of charging with the Onan gets them back to 90+% of capacity.

I have lead acid batteries, and can’t comment on how to check AGMs.  With lead acid batteries, a cold cranking amps test and specific gravity of the electrolyte can help figure out what is wrong.

Do AGMs need equalizing???

Kent Robertson
S/V Kristy
Panama cell: +507-61171896
USA cell: 828-234-6819

On May 6, 2018, at 8:46 PM, olaf_renos@... [amelyachtowners] <amelyachtowners@yahoogroups. com> wrote:


Hello AMELians,


On Friday I was first time out on anchorage with my SM2K and wondered about the discharging of the batteries. The discharging was around 20% within 6 hours! Only the fridge, refrigerator (on level 2) and the VHF were turned on. No more.


Furthermore, the wind generator was running all the time and the solar panel filled at that time as-well.


I my opinion this isn’t normal and I guess as minimum one battery isn’t working properly.


I also wondered about the charging of the Onan Generator. I run it with 100Amp charger and it could only fill up the batteries by ca. 2% in 1,5 hours!


What is the best way to find out what is wrong? Checking the batteries? How to check them if they don’t work properly?


My questions are now:

·        Is that the normal charging rate of the Onan generator by using the 100Amp charge controller with those kinds of batteries?

·        How is the normal charging rate of the Onan generator with those kind of battery setup?

·        Or do I have an issue with the Onan generator? When that seems to be how could I find out / what I have to check?

·        How could I find out or what is the best way to find out if the batteries are working properly or not?



AGM batteries Vision EV-27-AM and the capacity of each one is 100 Ah = 600Ah.


Solar Panel 245W


Wind Generator Silent Wind 400



Any help is highly appreciated.


Fair Winds


Olaf Bauer


S/V Sayonara II, SM2K 392

currently in St. Anne, Martinique