Only taken 7kw on overnight charge

[Phevanna]

Hello guys,

I am looking to buy a 2017 GX4H with 72000 miles.
On add pictures shows a picture of charging cost screen, I can see it is charged every day and dividing kw/h cost by total cost of charge I was able to find it is only taking 7kw per charge, seems pretty low, is that a sign of bad SOH? Should I stay way from it?
I know the battery still on warranty (8 years/100.000miles) but will be a lot hassle get it replaced if needed no?

Opinions please.

 

[Daixiwen]

The car only uses about 70% of the actual battery capacity, so a full recharge on a new battery would take about 9kWh. The question is whether the owner does a full recharge each day or not. If the car is not driven that much and the battery state of charge is still 40% when the charger is connected then it will only charge about 7kWh on a new battery.

Unfortunately the only way to know the battery's estimated SOH is to connect a OBD dongle and get the value from the BMU.

 

[Phevanna]

Thanks Daixiwen,

Yeah, apparently he leaves overnight every day which will be full charge.
My calculations is 7kw will be below 65% SOH.
I will bring my obd and if he let me check the battery I will do.
Just trying to figure out before engaging on a two hour drive to see the car.

 

[littlescrote]

kWh, not kW. There's a big difference, and it's useful to learn the difference.

 

[Phevanna]

kWh, not kW. There's a big difference, and it's useful to learn the difference.

On change cost screen I have:
kWh cost: £0.14
Total cost of last charge: £0.99

Am I wrong saying the battery took 7Kw?

Battery capacity: 12kw
7kw is around 60% if it, no?

 

[AndyInOz]

Hiya,

This may help distinguish between kWh and kW:

https://www.power-sonic.com/blog/kw-vs-kwh-explained/

In a nutshell kilo Watt hour (kWh) is the rated capacity of your battery.

Whereas kilowatts (kW) are an instantaneous measure of how much power is being consumed.

In this case, your charger has consumed 7 (and a bit) kWh.

There is always some loss in charging a battery, estimates range from 10% to 20% depending on conditions, so that's worth considering too.
In other words consuming 7kWh at the plug may mean that the battery has received a top up of 5.6 kWh. (That's a high loss estimate in my opinion)

As others have pointed out, you wouldn't expect the battery to use a full 12 kWh to charge up, because the vehicle software defends the battery to maximise its life.

Similarly, if you don't know the starting point when the owner plugs it in, you don't know how much usable power was left in the battery before it was charged.

If the owner has run the car down to user zero (actual 30%) every working day because they have driven more than the battery mileage every day, that's a different case from a user that recharges from user 30% to full charge every day.

That information is probably the most important.

If the user uses 50% charge each day and tops up to 100% each night, you'd be seeing low power consumption in the charging history.

Do the screen shots give any indication of the starting point of the charge?

(Sorry about the user 0% and user 30% above, but the car doesn't tell the 'truth' about the battery, it only tells us about the bit that we're currently allowed to use. Behind the scenes the software manages the full capacity of the battery.)

 

[littlescrote]

kWh, not kW. There's a big difference, and it's useful to learn the difference.

On change cost screen I have:
kWh cost: £0.14
Total cost of last charge: £0.99

Am I wrong saying the battery took 7Kw?

Battery capacity: 12kw
7kw is around 60% if it, no?

Yes, you're wrong. Ignoring the numbers and dividing the units you end up with kWh. The time involved is not a factor.

For a start the on board charger of the Outlander is only something like 3.7kW, so to get 7kWh in there would take 7 kWh / 3.6 kW = 2 h. You have to be left with a unit of time after doing the division. 7 kW / 3.6 kW would just be 2. 2 what? It makes no sense.

As Andy says, the battery capacity is kWh. Always. Imagine the battery as a bucket, it can store 12 litres. The charger is a tap filling the bucket. if it fills at 6 litres/minute, it takes 2 minutes to fill the bucket. The confusing thing is that kW does not show you that it is really a measure of electrical flow and just a special unit for Joules/s. That would get really confusing if we used kJ/s for Power and then for Energy multiplied that by time and used kJh/s