Forum Discussion

milo's avatar
milo
Explorer II
Sep 06, 2020

Possible Addition of Second Battery

Howdy ... I need you solar guys help please with a couple of questions.
My current battery is a 5 year old Group 27 Duracell Ultra Marine/RV Deep cycle that is starting to run outa oomph. We use a portable 130W Poli-si 7.35A panel and a Morningstar SunSaver-10L controller to charge it with when boondocking. For DW & my style of dry camping (3-4 nights at a time), no inverter, very little water pump usage and limited lights on at night. it works extremely well keeping the battery charged as the battery never gets below 12.35 (volt minder) at night and the next day the panel has it recharged. If we have sun.
I'm thinking when time comes to replace the battery I would possibly add a second 12v so we could use more & not worry bout running to much out of the battery.
My question is...
If I add a second battery, is my solar panel & controller big enough to charge 2 group 27 12V deep cycle batteries? If not, what size panel & controller would I need?

Controller & Panel we have now.





Thanks
Milo
  • milo's avatar
    milo
    Explorer II
    Sep 06, 2020
    Thanks guys.
    I'm still in the beginning stages of what I wanta do. Battery still seems to be doing its job. I'm just thinking bout the future. One of the first things I did when we bought the 5'er was convert all the inside bulbs to LED's. The panel runs up in the mid 14's for several hours, then tapers back to the mid 13's as it got the battery back to 100% or close to it. Was curious bout what we have now, if it would charge an added battery. Have thought bout 2-6 volts.
    Thanks for all your inputs.

    Milo
  • jdc1's avatar
    jdc1
    Explorer II
    Sep 06, 2020
    theoldwizard1 wrote:
    You are better off with two 6V golf cart batteries. They will store more energy and will probably cost less.

    What you have for solar will charge just fine. Obviously it will take longer. Add a good batter monitor like a Victron BMV700.


    I like it! Costco golf cart batteries....$99ea.
  • wa8yxm's avatar
    wa8yxm
    Explorer III
    Sep 06, 2020
    IF you are going to add. How about poppign for a pair of GC-2
    Logic
    Current battery is just under 100 AH and only about 20-25 usable (new)
    adding a 2nd doubles that

    A pair of GC-2 in series. 220 AH and 110 usable. that's twice the power storage for almost exactly the same price.

    YOu may find that the solar charges very slowly but .... slow is better.
  • MrWizard's avatar
    MrWizard
    Moderator
    Sep 06, 2020
    Same amount of use, means same amount of recharge needed
    Your 130w will be doing the same amount of work
    But your batteries will maintain a higher state of charge
    No problems, unless your usage increases beyond what your solar can provide
  • time2roll's avatar
    time2roll
    Nomad
    Sep 06, 2020
    The existing solar is fine with two batteries. The existing solar may produce even more power as it may be running flat out all day instead of tapering off as you reach full charge. Worst case get more solar if you find it is necessary. If your lights are incandescent I would replace with LED first.
  • theoldwizard1's avatar
    theoldwizard1
    Explorer II
    Sep 06, 2020
    You are better off with two 6V golf cart batteries. They will store more energy and will probably cost less.

    What you have for solar will charge just fine. Obviously it will take longer. Add a good batter monitor like a Victron BMV700.
  • Lwiddis's avatar
    Lwiddis
    Explorer II
    Sep 06, 2020
    Determine the AHs you use or want to use. Select a battery or batteries at least double that number. Better 2.25 or 2.50. Solar watts need to at least equal the total AHs. Select an adequate controller. Do it once, do it right.
  • 2oldman's avatar
    2oldman
    Explorer II
    Sep 06, 2020
    For your style I don't see any charging necessary if you start at 100%.
  • Lwiddis's avatar
    Lwiddis
    Explorer II
    Sep 06, 2020
    Starting ratio is one solar watt for every battery amp hour. On very sunny days, you’ll be ok.
  • pianotuna's avatar
    pianotuna
    Nomad III
    Sep 06, 2020
    Hi,

    Consider an SiO2 battery. A single 100 amp-hour would give you more usable power than two group 27 jars. Google SiO2 battery usa.

    My first solar system was 30 watts. It was enough to top off two group 29 batteries when in storage so every trip started with a full battery bank.

    The minimum would be 60 watts per 100 amp-hours.

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