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Thread: Start up and performance benefits of dual batteries?

  1. #1
    Member McOtto's Avatar
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    Start up and performance benefits of dual batteries?

    I know there are numerous forum postings on battery options. I have reviewed many of them. Sorry for adding another.

    The previous owner of my 72 911T installed a single Sonnenschein A512/40 A battery (40 Ah nominal capacity). It holds a charge and functions properly, but it is 10 years old. Because of its age, I am contemplating purchasing two new Sonnenschein A512/40 A batteries, installing them in parallel as Porsche intended, resulting in 80 Ah nominal capacity.

    On their website, Patrick Motorsports recommends an Odyssey two-battery set up which reportedly brings faster, reliable cold startup. Additionally reporting increased ignition output allows the MFI Porsches to take full advantage of the higher ignition output, resulting in better combustion, smoother performance, and lower emissions.

    That sounds impressive and appealing. My question is has anyone with MFI experienced a noticeable and material change in start up and running performance when using dual batteries versus a single unit?

    Thank you!
    1972 911T Targa
    1985 911 Carrera (with circa 1988 RUF 3.4L 260 hp DIN Engine Kit)

  2. #2
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    The '73RS lightweight only has one battery , so it seems Porsche did not think performance was compromised .

  3. #3
    Senior Member lopena's Avatar
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    No.

    I went from a single Optima Red Top to two Miata-sized batteries in my stock ‘69 911S and noticed no difference in starting or performance.

    Alan
    N.J.
    Alan
    N.J.


    1964 E-Type roadster
    1969 911S
    1988 328GTB
    2002 Maranello

  4. #4
    Member McOtto's Avatar
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    Very useful feedback. Just what I was looking for. Thank you!
    1972 911T Targa
    1985 911 Carrera (with circa 1988 RUF 3.4L 260 hp DIN Engine Kit)

  5. #5
    Member McOtto's Avatar
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    Thanks again everyone! I appreciate the great feedback from this forum, as well as Pelican’s. Takeaways appear to be:


    A.) No material start-up or performance benefits associated with two batteries versus one.

    B.) If you are an ice cream getter on Saturday night, cars and coffee on Sunday morning, and can’t drive without my prescription glasses guy (like me); and not a two-year GT3 champion (like Scott Winder), two-battery weight distribution is of no meaningful consideration.

    C.) If I want a two-battery set up because it is original, do it and shut up. Otherwise, a single battery is just fine.
    1972 911T Targa
    1985 911 Carrera (with circa 1988 RUF 3.4L 260 hp DIN Engine Kit)

  6. #6
    Quote Originally Posted by McOtto View Post
    C.) If I want a two-battery set up because it is original, do it and shut up. Otherwise, a single battery is just fine.
    Exactly this. I had dual batteries in my car for years and when they went a couple years ago, installed a single. Cannot tell the difference whatsoever.

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