Recommend a 12V battery please

[Iain]

Short runs don't make much difference to an EV. It hasn't had to pump out 3 or 400 amps into a starter motor to get the engine running. all it has to do is fire up the computer and flick the switch on the main battery.
A booster jump starter doesn't need to be expensive. You can pretty much buy the cheapest on amazon and it will be fine. As long as you charge it up each time you use it there isn't much to remember.

Thanks for your response Kevin.
Although I am no mechanic I am pretty sure my battery is not performing as well as it should.
I accept that the 12V battery does not have to pump out the large current that an ice car requires to start it but I suspect the cold weather, heating, lighting and wipers on during a twenty minute run is insufficient to keep the 12V battery in peak condition.
My (perhaps flawed) logic tells me;- 1 Change the battery at £70 to £100 pounds cost. 2 Ask the garage to check for faults £100 plus. 3 Buy a battery booster at £30 to £100 pounds.
Options 2 and 3 may still result in me having to buy a new battery so option 1 seems best.
Happy to be corrected if my old illogical brain is failing as fast as my battery.

 

[MickeySw]

but I suspect the cold weather, heating, lighting and wipers on during a twenty minute run is insufficient to keep the 12v battery in peak condition.

During a 20min run a healthy aux battery will be topped up sufficiently to keep its charge even in cold weather until the next day.

As already mentioned when driving (or charging) the 12V battery is not doing any work (the opposite actually) as all low voltage power is provided by the HV battery via a DC/DC converter.

1st step is indeed replacing the aux, but if your troubles don’t go away, suspect a dodgy CCU or ‘parasitic drain’

 

[kevin ellard]

Thanks for your response Kevin.
Although I am no mechanic I am pretty sure my battery is not performing as well as it should.
I accept that the 12v battery does not have to pump out the large current that an ice car requires to start it but I suspect the cold weather, heating, lighting and wipers on during a twenty minute run is insufficient to keep the 12v battery in peak condition.
My (perhaps flawed) logic tells me;- 1 Change the battery at £70 to £100 pounds cost. 2 Ask the garage to check for faults £100 plus. 3 Buy a battery booster at £30 to £100 pounds.
Options 2 and 3 may still result in me having to buy a new battery so option 1 seems best.
Happy to be corrected if my old illogical brain is failing as fast as my battery.

3. Should come first. After that, I agree that you might as well change the battery - its cheaper than taking it to the dealer to be examined.

 

[Gomev]

During a 20min run a healthy aux battery will be topped up sufficiently to keep its charge even in cold weather until the next day.

As already mentioned when driving (or charging) the 12V battery is not doing any work (the opposite actually) as all low voltage power is provided by the HV battery via a DC/DC converter.

1st step is indeed replacing the aux, but if your troubles don’t go away, suspect a dodgy CCU or ‘parasitic drain’

Is that correct ? I thought that the 12v battery supplied all the 12v functionality to the dash display. wipers, lights etc whenever they were on and the DC/DC converter merely supplied the power to the 12v aux battery. So the battery would be discharging and charging when driving.
I am happy to be wrong on this as it's useful info.

 

[MickeySw]

I am happy to be wrong on this as it's useful info.

A working DC/DC powers all low voltage circuits (including the 12V aux). Because the DC voltage is higher (around 14V) than the aux battery’s (12ish) current will flow into it (aka charging).

 

[Gomev]

A working DC/DC powers all low voltage circuits (including the 12V aux). Because the DC voltage is higher (around 14V) than the aux battery’s (12ish) current will flow into it (aka charging).

If this were the case what purpose does the 12v aux serve other than starting the car ?

From the interweb conflicting versions:

In an electric vehicle (EV), accessories like lights and windscreen wipers are powered by a standard 12V auxiliary battery, similar to those found in petrol and diesel powered cars.
The electrical architecture of an EV typically consists of two main systems:

• Low-Voltage (12V) System:This powers all standard "accessory" systems, including:
  • Exterior and interior lights.
  • Windscreen wipers and washer fluid pumps.
  • Infotainment screens, dashboard displays, and sound systems.
  • Safety features like airbags, central locking, and security alarms.
  • Onboard computers that "wake up" the vehicle and manage the high-voltage system.
• High-Voltage System: This primary battery pack (typically 400V to 800V) is dedicated almost exclusively to the powertrain (driving the motor) and climate control systems like the AC compressor.

How the 12V Battery is Charged
Unlike traditional cars that use an alternator driven by an engine, EVs use a DC-to-DC converter. This device takes high-voltage electricity from the main traction battery and "steps it down" to roughly 12–14 volts to keep the auxiliary battery charged while the vehicle is running or plugged in.

the interweb also says the function of the DC to DC converter is

Key Functions:

• Voltage Step-Down: Converts high-voltage DC (HVDC) from the main battery pack into low-voltage DC (LVDC) for the vehicle's subsystems.
• Powering Accessories: Supplies power for headlights, wipers, infotainment screens, sensors, fans, pumps, and other standard car parts.
• Charging the 12V Battery: Keeps the smaller 12V battery topped up, which is essential for starting the car and running safety features when the high-voltage system is off.
• System Management: Manages energy flow and can perform pre-charging and active discharging functions for other high-voltage components, ensuring safe power-up and shutdown.

Just goes to show you can't rely on the all knowing and artificial definitely not intelligence of the interweb.

Personally I'm going for option 1 above as it seems to be too complicated to have 2 power sources for the cars accessories rather than the traditional one of charge the 12v, by either alternator or DC/DC and then let that do the work..

 

[MickeySw]

If this were the case what purpose does the 12v aux serve other than starting the car ?

None, as long as the DC/DC is operating (READY or charging).
Loosing the DC/DC when driving would shut the car down immediately, in that case the 12V acts as a backup

Personally I'm going for option 1 above as it seems to be too complicated to have 2 power sources for the cars accessories

There are indeed two power sources but they operate at different times..

 

[Gomev]

None, as long as the DC/DC is operating (READY or charging).
Loosing the DC/DC when driving would shut the car down immediately, in that case the 12V acts as a backup

There are indeed two power sources but they operate at different times..

So are you saying that once the car is in ready state you could disconnect the 12v and the car would still run with the DC/DC operating all the ancillary equipment ?

 

[Alb]

That should work in principle but the car might flag the missing battery as a fault condition.

 

[Gomev]

That should work in principle but the car might flag the missing battery as a fault condition.

So the only purpose of the 12v is to start the car ! Well, well, well.
Manufacturers may as well abandon the12v battery, leave the car permanently in ready state but with some form of security required, such as a key or code etc, to engage drive modes.

 

[MickeySw]

Manufacturers may as well abandon the12v battery,

It’s already happening, some EV models use a DC/DC only..