AGM batteries old—time to replace?

[Blueboy#1]

I’m pretty new to my 2019 R-27 outboard and I think the pair of house Interstate AGM 31-AGM7 batteries probably need replacing.

I did some simple practical tests: I turned off shore power and all devices except the galley fridge and whatever background systems run like the Propane sensor and switch (but in standby off position), inverter switch lamp, CO monitor, etc.

Then the solar controller readout for my twin 195watt solar panels (390watts total) showed
charging the house and engine and thruster batteries to between 13.99 and 14.5 volts. The solar readout photo attached.

The Victron Battery sensor readout was 13.99-14.3volts—at 2pm on a partly sunny day—all seemed good.

I covered the solar panels to simulate nighttime and turned on the Webasto diesel heater—it fired up and ran great with Victron showing 13.7V starting off. But within 30 minutes the heater shut down and when I went to check the Webasto display it read: “maintenance required low voltage”. Victron now read 12.7V. I don’t think the heater needs maintenance because it has run fine many times this winter when we’ve been on shore power.

I then uncovered the solar panels and let the 3-4 pm partial sun charge the batteries for an hour until the Victron read 12.89V and tried to start the heater again but no joy—low voltage message on the Webasto.

So unless I’m mistaken the two 31-AGM7 commercial grade marine house batteries need replacing—any knowledgeable person please chime in with any comments.

In addition I will probably replace the engine and thruster batteries because during the power down from the shore power they started at 14.4V when the solar panels were uncovered and charging, but the readings fell to 12.8 with the solar panels covered (off) and the fridge and heater working. The voltage for these batteries rose a little when the heater was turned off but still only 12.7 before I uncovered the solar panels and allowed the charger to run. Not sure what kind of batteries they because they are tucked in tight in the after part of the starboard cockpit locker under the entry port deck. I think they are 24 group size AGM batteries but I can’t tell until I remove them from the system. Is it best practice to have all house and all engine batteries AGM?

Any comments, suggestions, criticisms, brilliant solutions or advice are welcome and appreciated! Thanks to all the folks who have been so great and helpful already in this community.

 

[SKing]

Consider adding a Victron shunt when replacing your house batteries. It will remove all the guessing in the future. If you haven't read up on them yet, there are lots of posts as well as good articles on line

 

[Blueboy#1]

Thank you Steve and Michelle for your help!

 

[CapBonnieB]

It is not clear that you do need new house batteries. It’s not unusual for the battery to show 14+ volts when charging and then high 13+ volts just after coming of a charger. The batteries will then drop to a little less than 13 v even with no use. On the other hand, per Martin ,spreadsheet , the heater pulls 20 watts or 1.67 amps. That’s less than the refrigerator. So running the heater for 30 minutes should not have been an issue. If the shore power and battery charger is on, does the heater still continue to run fine - say a hour or more. I know you said it did before but just to confirm that the heater didn’t suddenly develop an issue. It would have been good to see the battery voltage just prior to heater shut down.
How old are the house batteries?
Yes replace the house batteries as a pair at the same time when you do replace them
I F you stay with lead acid batteries, then yes AGM are your best choice. If you go to lithium you will need new batter chargers.
Martin is familiar with your heater and both the old AGM batteries and the new style Lithium batteries so Martin will probably also jump in here to help.

 

[venajeff]

I my experience with lead acid batteries, if you are having any electrical issues and you haven't just recently replaced the batteries then start by replacing the batteries. I have installed new alternators because the battery was tested and was "fine", to find out that it was the battery.
Also, I discovered that if you need a battery and Costco carries it, you won't find it cheaper anywhere else. And the savings will probably pay for the membership and more.