When to use battery tender

Discussion in 'Technical Q&A' started by Circle K, May 10, 2021.

  1. Circle K

    Circle K Karting

    Dec 21, 2017
    Full Name:
    How long does the car need to sit before using a battery tender? Curious if my Ferrari is draining the battery faster than it should?
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  3. EastMemphis

    EastMemphis Formula Junior
    Silver Subscribed Owner

    May 25, 2019
    Memphis, TN
    Full Name:
    When I first got my 360, I poo-poo'd all the advice of using a tender. I did buy one but didn't use it. After about six months, I started to get odd problems with the electrical, such as weird operation of the windows and capote. I started using a tender and the first time I used it, it took at least a day before the battery was fully charged. I started using a tender religiously since then and I've had no electrical surprises since.

    My theory is that the alternator just keeps up with the drain on these cars and when a tender isn't used, the battery gradually gets depleted to the point that sufficient voltage is no longer present for the systems on the car to operate properly.

    So in answer to your question: The car should always be on the tender when not being driven. If you suspect you have an excessive parasitic drain someplace in the car, start by hooking up a multimeter that measures milliamps in series with your battery (with the key off) and see how much juice is being drained when the car is parked. It should be less than 100 mA. If you see high readings, then your next step is to start testing individual circuits at the fuse to see which is causing the drain. From there, it's just a simple matter of advanced surgery and technical wizardry to solve the problem.
  4. innerloop

    innerloop Formula Junior

    Jan 17, 2010
    Houston Heights, TX
    I agree with EastMemphis. I put the 348 on the charger whenever it is parked. I have the cord hanging down from the ceiling right above the left front fender which is where my battery is located. Each time that I get home I just pop open the front trunk and plug in the pigtail. No problems and I've been on the same Optima Red Top battery for at least 14 years.
    AndreB and EastMemphis like this.
  5. Jason Frye

    Jason Frye Rookie

    Oct 12, 2020
    Parker, CO
    Full Name:
    Jason Frye
    If you aren't driving it, put it on the tender. Even when I daily mine, as soon as I'm home I plug her in. It takes 5 seconds. I figure, why not!?
    Circle K and EastMemphis like this.
  6. mattexplore

    mattexplore Rookie

    Mar 1, 2021
    Prescott, Arizona
    Full Name:
    Matthew Scott
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  8. 2dinos

    2dinos F1 Rookie

    Jan 13, 2007
    I'm a tender / maintainer believer.

    I've had a battery just outside warranty go flat in storage. I was intending to replace but Interstate store recharged at no charge (Pun intended - don't know??) and told me "it recovered fine and is good as new". I'm pretty certain it didn't crank as well as it used to, before going flat.

    i.m.h.o. With maintainer, it's always fresh.
  9. miketuason

    miketuason F1 World Champ
    Silver Subscribed Owner

    Feb 24, 2006
    Cerritos, CA.
    Full Name:
    I use mine all the time.
  10. tomc

    tomc Two Time F1 World Champ

    Apr 13, 2014
    DFW, Texas
    Full Name:
    Tom C
    I like putting it on the tender always - I drive our F-car 2 or 3 times a week - if for no other reason than it gives me a little gauge on battery health. I have a CTEK 7002, and there are 4 lights - light 1 comes on immediately, light 2 comes on in 10 sec, light 3 in about 10 min, light 4 (green) in about an hour.

    How old is your battery? How old is the tender?

    alex likes this.
  11. Ak Jim

    Ak Jim F1 Veteran
    Rossa Subscribed Owner

    Dec 23, 2007
    North Pole AK
    Depending on the electronics in the car another option is to disconnect the battery.
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  13. Ferrari Tech

    Ferrari Tech Formula Junior

    Mar 5, 2010
    Full Name:
    Wade Williams
    I agree with plugging in the tender when you park it. Keep it totally fresh. That one time you don't plug it in and then don't get back to it for two weeks and its flat. Not worth it as you may chase issues after that.
    On another note, I have always gone with 25 mA max for a battery draw. 100 mA will kill a battery very fast.
    Still, just plug it in.
  14. ttforcefed

    ttforcefed F1 World Champ
    Rossa Subscribed

    Aug 22, 2002
    new feraris, anything more than 3 days. my 355 can go weeks.
  15. Ricambi America

    Ricambi America F1 World Champ
    Sponsor Owner

    Every. Time. You. Park.
  16. ttforcefed

    ttforcefed F1 World Champ
    Rossa Subscribed

    Aug 22, 2002
    For cars sitting more than a few weeks I disconnect the batteries.
  17. Drew Altemara

    Drew Altemara Formula 3

    Feb 11, 2002
    Tuscaloosa, AL
    Full Name:
    Drew Altemara
    Always tendered when parked as well.
  18. JCR

    JCR F1 Veteran
    Silver Subscribed

    Mar 14, 2005
    H-Town, Tejas
    Not only Ferraris but all modern cars in general. They are full of microprocessors that never really turn off and that is your parasitic drain.
    f355spider and Circle K like this.
  19. Tegethoff

    Tegethoff Karting

    Jul 19, 2014
    Los Feliz
    Full Name:
    BMW's internal electrical monitoring system even judges you with a "unfavorable driver profile" in diagnostic reporting, long storage times, short trips, multiple engine starts, etc are all detrimental to battery life.

    I plug in a tender if I know it will be more than 24hrs before I drive again, but for a infrequently driven car, just do it every time it makes life easier.
    f355spider and tomc like this.
  20. f355spider

    f355spider F1 World Champ
    Rossa Subscribed Owner

    May 29, 2001
    I've basically come to the conclusion that any of my cars (or motorcycle) that are not going to be driven in the following week, should be plugged in. If I an unsure if it will be driven, plug it in. Ultimately, if it isn't much trouble...just plug it in as a matter of course.
    Circle K likes this.
  21. f355spider

    f355spider F1 World Champ
    Rossa Subscribed Owner

    May 29, 2001
    I have a BMW G30 M550iX, and there are two AGM batteries. One in the trunk and one in the engine compartment. Apparently the one in the engine compartment is for the "start/stop" functions. I try to ensure I put the battery tender on them both periodically. At least the charging access for both is through the engine compartment, which simplifies things. I learned from BMW, if I charge the main trunk battery through the "jump start" charging connections in the engine compartment, the car's battery monitoring system isolates the "start/stop" battery and it must be connected separately.

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