Flat battery

Discussion in 'Electrical' started by TomH65, Jan 10, 2016.

  1. TomH65

    TomH65 Active Member

    If a bike battery is totally flat due to being stood over the winter, can the bike be started safely by hooking up a charged battery to the flat one then once started, unhook the charged battery and allow the alternator to charge up the one already in the bike?
    Or is it best to remove the battery, charge it and replace it?
  2. Dr. Dolittle

    Dr. Dolittle Experienced Member Staff Member Moderator Contributor

    The first option sounds like it may put a lot of stress on the charging system and maybe cause a problem in that area. I would vote for a new battery.
  3. dolt

    dolt Senior Member

    The OP failed to mention how old the batter is. If 4-5 years old, I would toss it and replace with a quality AGM battery; simple, one and done.

    However, if only a year or two old, pull the battery, take it to Advanced Auto or Auto Zone and have it load tested. If the load test shows the battery to be serviceable, put it on a charger (not a trickle charger) until fully charged and reinstall. By serviceable, I mean meeting the original performance specs for that battery; anything less, toss it. It will just fade away and likely leave the OP stranded somewhere. If the battery tests out OK, reinstall and keep the battery on a tender at all times after that and the OP might get another two years out of the battery.

    It is not easy to bump start these vtwin motors, if there is any doubt about the integrity of the battery, replace it and avoid getting stranded somewhere. Get a tender and keep which ever battery used on a trickle charge at all times. A new battery kept on a tender will last five years under most circumstances.:s
  4. Jack Klarich

    Jack Klarich Guest

    Any thing new to report? If you junp the battery make sure the donor battery is hooked up clean and donor engine not running
  5. TQuentin1

    TQuentin1 Well-Known Member Staff Member Moderator

    The bike runs off the battery with the charging system there to keep the battery as charged as possible. Running on a mostly discharged battery will put a significant load on the charging system. Better to remove the battery from the bike and fully charge it, then load test it to make sure it is OK to use. If fully charged and a go on the load test, reinstall. Otherwise replace with new battery. Consider using a Battery Tender (Jr.) to keep battery fully charged when not in use.


  6. Iceman24

    Iceman24 Well-Known Member

    My vote = pull old, charge, install & try to start. If this doesn't do the trick...might be time for new juice.
    Vettster likes this.
  7. Jack Klarich

    Jack Klarich Guest