Too Many Batteries?

rp3703rp3703 Registered Users Posts: 115 ✭✭

I have one more question about battery storage and then I think I'll be done asking questions for now. I have calculated my loads at 2272 WH/Day. Using a formula I got on their site fro BB 

”WH/Day x 1/0.85(inverter efficiency) x 1/Battery Voltage x 2 Days of Storage x 1/.5 Max Discharge=AH”, that comes out to 430 AH of battery storage required for two days of zero sun. 

Eight 6V 215 AH Deka batteries wired in series parallel will give me exactly 430AH but I have mistakenly purchased 4 more for a total of 12 which would give me 645AH. 

Should I return these four extra batteries or would it be worth it to have the extra AH just in case. I’m guessing the formula used to figure AH is probably a worst case scenario to allow enough power to make it through cloudy winter months. I will only be using these batteries from June to August in Northern Ontario. 

I’m also worried that the more batteries there are, the harder it will be for my charge controller(Classic 150) to keep them equalized. Plus operating on 8 batteries instead of 12 will be cheaper when it comes time to replace them.

1860 W (6) Rensola JC310M, Classic 150, [email protected] (8) Deka DSGC15 FLA's, Victron Phoenix Multi 24/2500 Inverter
Powering-20.5 CuFt. Fridge, 1 HP Submersible water pump, UV, Washing Machine, Gas Dryer, Gas Stove, Lights and Receptacles
Off Grid Cottage on lake in Northern Ontario 46˚N 


  • EstragonEstragon Registered Users Posts: 3,127 ✭✭✭✭✭
    I'd recommend returning the extra batteries for a number of reasons:

    - You're correct that to much storage vs charging capacity is likely to result in undercharging and short battery life.

    - Having more than two strings means having to fuse each string individually.

    - More strings are harder to wire properly (strings need equal charging and discharging, or can get unbalanced capacity and shorter life).

    - Last but not least, a first bank can be a casualty of misestimated loads, installation issues, etc. Better to minimize the cost of a mistake ;-)
    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
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