Concerned about my 3 year old AGM marine batteries

markabncmarkabnc Registered Users Posts: 2
I have a small solar setup that has been working great for 3 years.
Morningstar Tristar MPPT 45
5 x 100 watt mono panels in series
2 Deka marine batteries in parallel - I got the marine batts because live near a lake and felt I was getting a good deal on them.  I also wanted AGM because they stay inside.

Here's my question... When everything was new I would have a resting voltage in the evening of 12.8 - 12.9 volts.
Now it is consistently 12.6.  Is this normal for older batteries.  They still seem to have the same capacity etc.


  • EstragonEstragon Registered Users Posts: 4,496 ✭✭✭✭✭
    A resting voltage of 12.6 suggests the battery isn't getting fully charged (or possibly a measurement issue) to me.

    I'd check voltage on each battery separately as one may be getting chronically undercharged vs its twin, and require periodic remedial charging on its own.

    If both are about the same, I'd look at charging regime.  Are they getting to the recommended absorb voltage (likely ~14.5v) and staying at that voltage for 2-3 hrs in the charge cycle?
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • jonrjonr Solar Expert Posts: 1,386 ✭✭✭✭
    Logically, as batteries age and get some permanent sulfation, you aren't going to get the same peak voltage (because the acid is weaker).  Trying to push it higher will only cause more wear.   There should be some corresponding capacity loss,  but you might not notice it.

    So IMO, could be lacking of charging (this is December) or aging.

    I am available for custom hardware/firmware development

  • mike95490mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    I'd also suspect that 3 year old marine AGM are reaching end of life.  What's the factory warranty on yours?
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    gen: ,

  • markabncmarkabnc Registered Users Posts: 2

    Thanks for the comments. I think the warranty was 1 year.

    I check and the charging parameters are set to the East Penn recommendations.

    And yes it has been a rainy winter.

Sign In or Register to comment.