Charging 12V Battery While Attached to the Car

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by Jonny Zero, Dec 31, 2012.

  1. Jonny Zero

    Jonny Zero Giggidy

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    It seems that many here charge the battery while it us still hooked up to the car. The manual, however, warns that the negative post should be disconnected before charging. I do not like to do that for no other reason than the car loses all the presets.

    I have always charged my conventional cars with the battery attached. What is the reason for asking for the 12V to be disconnected before charging in a Prius? I know there are a lot of electronics, pumps, connected to the 12V circuit even while the car is off. Any real world harm done with charging with the 12V still connected to the car?
     
  2. Britprius

    Britprius Senior Member

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    I believe Toyota are covering all the bases by warning to disconnect the battery before charging.

    It does help protect the ECU's from voltage spikes and to be fare that is a good thing to do.

    The problem arises with some modern chargers with a desulphator systems built in. These often work by pulsing high voltage spikes into the battery to brake up the sulphation and these could easily damage an ECU.

    Having said all that I cannot see a small battery tender doing any harm. Others may disagree.
     
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  3. Mendel Leisk

    Mendel Leisk Senior Member

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    I've hooked up a CTEK 3300 multiple times, without first disconnecting the battery. It has a desulph... phase in it's charging cycle. So far so good.
     
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  4. Britprius

    Britprius Senior Member

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    I would like to see the output of that on a scope.
     
  5. Braddles.au

    Braddles.au DEFAnitely using an EBH

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    Supplementary question, would you top-up the battery while it is in-situ? Under the covers? Is there sufficient ventilation?
    Frustrated by 2 weekends in a row with a weak battery I invested in a Ctek MXS 5.0 charger and a 'Comfort Indicator' with green, yellow and red lights to indicate the SOC (>80%, 60-80%, <60%). I attached the leads to the battery terminals and positioned the connector stuck to the inside of the boot so that I can see the flashing light from outside, even with the tonneau cover on.
    [​IMG]
    To charge I plug the charger into the connector without removing any of the covers. I'm using the charger with the hatch open, but all covers in place. I'm considering a 3.3m COMFORT INDICATOR PANEL that would give me and indicator and socket on the lower dash. I could see the SOC and plug the charger in easily through an open front window.
    BTW if I was performing an annual "recon" charge then I'd take the battery from the car and charge it on the bench.
    EDIT: Based on BritPrius' advice, I'll leave the battery in at all times, if there's no dissenting opinions?

    UPDATE: The indicator is yellow every morning, indicating between 60-80% SOC. Either it's not getting near 100% during driving since its last dip or there's a reasonably big drain overnight.
     
  6. Britprius

    Britprius Senior Member

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    The Prius battery is designed to be charged at 4amps maximum. At this charge rate the battery should not gas externally, but recombine any gasses produced internally turning them back to water, stopping the battery drying out.

    There is a vent tube from the battery to the underside of the car in case the battery does vent. If you do an annual charge on the bench it should not be at a rate above 4amps as this will cause the battery to vent starting the drying out processes.

    This only applies to the OEM battery, other batteries such as the Optima usually have a higher charge current limit "10 amps for the Optima with temperature monitoring".
     
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