Voltage Across The Battey Before Starting

Discussion in 'Bonneville' started by DGBland, Oct 15, 2021.

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  1. DGBland

    DGBland Member

    I tried to start my 2015 T100 Bonneville a couple of times lately but the battery appeared to be flat. It read 12.4 or 12.5 each time and after about half hour on the battery charger it was fine for the rest of the day.
    What should the battery voltage read when not running?
    It will just about start at 12.6 volt but won't at 12.5. The voltage drops in the cold during the winter but I should really be able to start it in the cold weather.
    I read on a recent post that lithium batteries don't like the cold. What is the best type of battery to buy?
    It charges well enough once running. I use the bike all year round and it has done 30,000 miles

    Thank you
    David

    20161029_153140-1.jpg
     
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  2. DGBland

    DGBland Member

    When the engine is running it charges ok so yeah I think I need a new battery
     
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  3. KC1961

    KC1961 Member

    Nov 13, 2014
    55
    18
    West Lothian
    I had to replace the oe battery on my similarly aged bike a few months ago, maybe this is just about as long as they live?
     
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  4. Pegscraper

    Pegscraper Elite Member

    Jun 12, 2020
    2,932
    800
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    A fully charged LA battery is 12.6v (6 x 2.1v cells). Voltage drop under load is the measure you should look at as a knackered battery can still show 12.6v. Personally I'd go with a Yuasa or Varta battery.
     
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  5. Cyborgbot

    Cyborgbot Guest

    The voltage is half the story. The amps the battery can sustain (cranking) is v important.

    Lithium batteries don’t like the cold however turn the ignition on (thus lights) for a few seconds whilst you don your lid and gloves then it will ‘activate’ and work as normal.

    Most people don’t do this (or notice issues) as it’s normally pretty harsh conditions that need to activate the battery and most people would just take their car or wrap up warm under a blanket in front of a roaring fire.
     
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  6. Pegscraper

    Pegscraper Elite Member

    Jun 12, 2020
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    The voltage drop tells the story. The cranking amps rating of a battery will drop with the voltage as the current is directly proportional to the voltage and inversely proportional to the resistance (of the load).
     
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  7. Pegscraper

    Pegscraper Elite Member

    Jun 12, 2020
    2,932
    800
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    That is one clean looking Bonnie!:)
     
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  8. Cyborgbot

    Cyborgbot Guest

    Yeah - which is why the RAC have expensive ‘load’ testers and not just volt meters.

    A low voltage but high current will still crank an engine. A high voltage and low current won’t.

    A battery is made of multiple cells. Voltage alone will not indicate the health of each individual cell and can mask other problems.
     
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  9. Cyborgbot

    Cyborgbot Guest

    Or maybe you have a different type of electricity to me ;)
     
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  10. Pegscraper

    Pegscraper Elite Member

    Jun 12, 2020
    2,932
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    It's basic Ohm's law. It's the current which turns the motor or lights the bulb, it's the voltage that "pushes" the current through the resistance. A 6v 500CCA battery wouldn't turn over a 12v starter as the voltage is too low to deliver the required current through the starter' resistance. All a load tester does is put a known load on the battery and measure the voltage drop and hence the available current.
     
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  11. Chainbiter

    Chainbiter Well-Known Member

    Aug 6, 2021
    104
    83
    North Yorkshire
    Just fitted a new battery on my Bonnie a couple of days ago, it never failed to start the bike but could tell it was getting sluggish.

    Also have one of these:

    https://www.motone.co.uk/triumph-bo...adlight-module-battery-saver-safe-start-p2028

    It stops the headlight from lighting up when you turn the ignition on, once the bike is running just flick to high beam and the back to low and the headlight then works normally.
     
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  12. Pegscraper

    Pegscraper Elite Member

    Jun 12, 2020
    2,932
    800
    Yorkshire
    The throb of my knob is such a rare occurance these days, the angle of dangle hardly changes.
     
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