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  1. #1

    Default 12v battery flat after three days

    December 2013 ED, 10K miles. Had a problem with the 12v battery yesterday. Had gone flat after the vehicle was parked up and unused for three days, yet plugged into the wall charger. The HV battery was at 100% SOC. Nothing was left switched on and the weather is hardly cold at the moment (Iíve found cold to be a real killer for lead-acid batteries).

    The Smart Assist Plus tech who came out recharged the battery for 20 minutes, checked it on load with a pukka tester and pronounced it 100%. He advised a couple of long journeys to charge it up fully.

    Maybe Iím being thick but surely that advice would only apply to an ICE car? I imagine (but donít know for sure) that the 12v battery in the ED is charged every time the car is plugged in, and then perhaps topped up from the HV battery as required?

    Iíve ordered a cheap fag lighter socket voltmeter to help keep an eye on the battery condition but wondered if it word be worth getting the on-board 12v charge circuitry checked out to avoid a recurrence?

  2. #2
    Join Date
    Dec 2016
    Location
    Hampshire
    Posts
    179

    Default Re: 12v battery flat after three days

    I have heard of this problem with other makes of electric and hybrid vehicles. It seems the 12V service battery is not usually charged when the traction one is on the mains. It only gets charged when the 'ignition' is on.
    There is also a double whammy in that because the service battery doesn't need to do engine starting it's usually of much smaller capacity that one in an ice car, so any small parasitic loads like alarms (or interior lights) drain it much faster.

  3. #3

    Default Re: 12v battery flat after three days

    Quote Originally Posted by dpmike View Post
    I have heard of this problem with other makes of electric and hybrid vehicles. It seems the 12V service battery is not usually charged when the traction one is on the mains. It only gets charged when the 'ignition' is on.
    There is also a double whammy in that because the service battery doesn't need to do engine starting it's usually of much smaller capacity that one in an ice car, so any small parasitic loads like alarms (or interior lights) drain it much faster.
    Hmmmm. The charging only when the ignition is on would certainly align with the problem and the Smart Assist recommendation. Many thanks for the observation. As well as the battery meter I'm also considering carrying a portable (in the ICE world) starter/charger unit to get me out of a similar hole. Though it does seem faintly ridiculous when there's nearly 18KW sitting right under the seats. There's also the added Catch 22 of not being able to turn on the ignition once the battery is flat, making external charging direct to the battery the only option.

  4. #4
    Join Date
    Jul 2005
    Location
    Aberdeenshire
    Posts
    1,627

    Default Re: 12v battery flat after three days

    Seems like poor design to me. Just read the following in the ed's handbook:

    If you use your vehicle mostly for short distance trips, you will need to have the 12 volt battery charge checked more frequently.

    That would indicate the 12 volt battery is only being charged whilst you drive.

  5. #5

    Default Re: 12v battery flat after three days

    Quote Originally Posted by tolsen123 View Post
    Seems like poor design to me. Just read the following in the ed's handbook:

    If you use your vehicle mostly for short distance trips, you will need to have the 12 volt battery charge checked more frequently.

    That would indicate the 12 volt battery is only being charged whilst you drive.
    The vast majority of our journeys are either 46, 35 or 26 mile round trips. But am aiming to push the envelope to 65 miles tomorrow (with a few charge points en route if required). It's a shame that Smart didn't think of providing an easy way to monitor the 12v battery condition given that it's every bit as important to vehicle operation as the HV battery.

  6. #6
    Join Date
    Dec 2016
    Location
    Hampshire
    Posts
    179

    Default Re: 12v battery flat after three days

    Quote Originally Posted by GeoffT View Post
    Though it does seem faintly ridiculous when there's nearly 18KW sitting right under the seats. There's also the added Catch 22 of not being able to turn on the ignition once the battery is flat, making external charging direct to the battery the only option.
    It does sound daft, but I suspect there are safety reasons around leaving the 12V battery being charged from a high voltage one while the car is unattended. That other manufacturers do it too means it may even be a legal thing.
    I think some people improve things by using one of those solar chargers which can live on the dash, but of course that's not going to fly if you keep the car in a garage.

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