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Thread: Backup battery self discharge

  1. #1
    Junior Member
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    Default Backup battery self discharge

    My airplane was in cold storage for 7 months this last winter (and I mean COLD - Fairbanks). When preparing for the summer flying season I checked voltage on both the Main (PC-680} and backup batteries. Main measures 12.5 V, a little down as expected after sitting so long. But the backup was only about 6 V??
    Put the backup battery on a dumb 2 V (constant voltage I think - Battery Tender Plus) charger overnight and it came up to 12.9 V. It has held at that level for several days since.
    So does the backup battery (new from CC last September) have a greater self discharge rate?
    Anyone have a similar issue?
    Thanks folks.

  2. #2
    Senior Member Andy's Avatar
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    Default Re: Backup battery self discharge

    Quote Originally Posted by jamiller View Post
    So does the backup battery (new from CC last September) have a greater self discharge rate?
    Anyone have a similar issue?
    Thanks folks.
    Assuming you are talking about the emergency ignition battery and not the IBBS battery used on G3X systems -

    The emergency ignition battery is SLA type and the "Panasonic Technical Manual - SLA"
    https://www.power-sonic.com/wp-conte...cal-Manual.pdf
    says:

    "Shelf Life & Storage

    Low internal resistance and special alloys in the electrodes assure a low self discharge rate and, consequently, a long shelf life. If kept at 20C (68F), about 60-70% of the nominal capacity remains after one year of storage. Due to the self-discharge characteristics of this type of battery, it is imperative that they be charged within 6 months of storage, otherwise permanent loss of capacity might occur as a result of sulfation.

    The rate of self discharge varies with the ambient temperature. At room temperature (20C (68F)) it is about 3% per month. At low temperatures it is nearly negligible; at higher ambient temperatures self discharge increases.
    To obtain maximum battery life and performance, batteries should be recharged as soon as possible after each use and not stored in a discharged state. If possible batteries should be stored at 20C (68F) or lower, and recharged every six months when not in use."


    If I were storing my FX-3 for 7 months I'd remove the batteries and charge them at least once a month. But no, I wouldn't expect the SLA emergency ignition battery to have a higher self discharge rate than the main SLA battery. The discharge of your battery seems to be abnormal given the low storage temperature.

    What was the voltage on the battery you removed (assuming you didn't discard it and it was stored in the same place as the airplane)?
    Last edited by Andy; 05-11-2021 at 09:03 AM.

  3. #3
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    Default Re: Backup battery self discharge

    Quote Originally Posted by Andy View Post
    Assuming you are talking about the emergency ignition battery and not the IBBS battery used on G3X systems -

    The emergency ignition battery is SLA type and the "Panasonic Technical Manual - SLA"
    https://www.power-sonic.com/wp-conte...cal-Manual.pdf
    says:

    "Shelf Life & Storage


    What was the voltage on the battery you removed (assuming you didn't discard it and it was stored in the same place as the airplane)?
    The backup battery (for the ignition) had a voltage of approx 6 V. Agree, I expected the backup battery to have discharged to about the same degree as the main battery. As I said, it charged right back up and has been holding at about 12.9 V for a week now. I cant figure out why it would have self-discharge more than the main battery. Note I didnt check the voltage of the backup battery when I mothballed the airplane last fall; it could have been seriously depleted already at that time for some unknown reason.
    I fabricated a jumper so I can easily monitor its voltage directly and without having to remove the front right interior panel and without having to rely of the system monitor. Im going to reinstall it and watch it carefully for awhile to make sure it gets charging voltage when the engine is running and that it holds its voltage between flights.

  4. #4
    Senior Member Andy's Avatar
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    Default Re: Backup battery self discharge

    Quote Originally Posted by jamiller View Post
    Im going to reinstall it and watch it carefully for awhile to make sure it gets charging voltage when the engine is running and that it holds its voltage between flights.
    The emergency ignition test should be a fairly good indicator of the battery condition as long as you keep emergency selected for at least 10 seconds and watch how the voltage behaves. The rate a which the voltage drops gives far more information than just checking there is no rpm drop.

  5. #5
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    Default Re: Backup battery self discharge

    Thanks. Ill try that.

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