MG5 Disappearing charge

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Geoffers

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Today I lost 9% of my charge with my pre-facelift 5LR sitting on the drive doing nothing.

The full story is this. I drove 175 miles to home from Bristol starting with 100% battery in good weather and temperatures around 8 Deg C. A good steady journey, mostly motorway at a 65mph cruise and arrived with 19% charge left and 44 available miles showing (actually pretty similar to my journey to Bristol a few days before). I was at home for about an hour and then had to pop to the local shop. I was surprised and peturbed to find at start up the available charge had dropped to 10% and 16 miles showing.

Anyone any idea where this charge disappeaded to? A bit scary to think I had about 10% less in the tank than I thought.
 
It probably recalculated the gom based on your last trip.
The car had also cooled down a bit, did you change the heat settings?
 
I can understand the gom adjusting. But % charge left should still be the same regardless. Unless OP is misremembering the battery %.

I would suggest battery balance could be to blame. The % left us based on the highest reading for any one module, if your battery hasn't has a balance change in a while you could get these wild swings at the bottom end of charge.
 
Thanks for the comments.

I am aware of the possible inaccuracy of the gom but I alway thought the % was pretty accurate. Infact on one occasion last summer I (accidentally) run down much lower than I intended while trying to find a charger and whilst it was a scary moment the gom and % seemed remarkably accurate at the very low level of charge I ended up with.

I understand the battery balance hypothosis, however (I hope) this should not be an issue as I only slow charge. I slow charged to 100% before my trip to Bristol and again while I was there for the return.

I was in KERs 3 and Econ when I stopped. But again I can see that possibly affecting the gom (not that it has ever done that before) but definitely not the %.

I will monitor very carefully!
 
Geoffers said:
Thanks for the comments.
snip/

I was in KERs 3 and Econ when I stopped. But again I can see that possibly affecting the gom (not that it has ever done that before) but definitely not the %.

I will monitor very carefully!
Click to expand...
Unless you put the car back into kers 3 before you looked at the soh then this is the issue. Try it when you are out and about, you'll see the range decrease/increase as you switch between modes, I've done the same myself.
 
5teep said:
Unless you put the car back into kers 3 before you looked at the soh then this is the issue. Try it when you are out and about, you'll see the range decrease/increase as you switch between modes, I've done the same myself.
Click to expand...
Range on the GOM sure, but the actual SOC %age indicator?
 
That's what I keep coming back to. GOM can and will change based on many factors. But battery % should not change.

Did you charge beyond 100% until the cells were fully balanced? If youre just unplugging when it hits 100% every time the cells will slowly go out of balance and, in theory, may result in this shift in battery charge %.

The recommendation is to balance charge monthly. I do mine more often, but I'm also putting in around 1200 miles a month so the battery is up and down like the proverbial essex girls drawers.
 
It possibly shows an out of balance battery. This can happen if you rapid charge a lot and don't charge to full on AC very often. It could also happen soon after rapid charging as the voltage settles. However it might indicate a weak cell so it might be worth a trip to the dealer to check the cell min/max voltages.
 
Petriix said:
It possibly shows an out of balance battery. This can happen if you rapid charge a lot and don't charge to full on AC very often. It could also happen soon after rapid charging as the voltage settles. However it might indicate a weak cell so it might be worth a trip to the dealer to check the cell min/max voltages.
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If you have an OBD2 dongle carscanner may show min and max cell voltage. (Does on my pre facelift 5)

I think I paid about £12 for the Wi-Fi one that works with iOS, I had an older bluetooth one that worked ok with android but not ios (Was too old for bluetooth LE).
 
Battery balance seems like the most likely answer at the moment. This thought is stirring around in my little brain - if batteries require balancing as a result of rapid charging, would they not require the same as a result of rapid dis-charging? My thinking is this, I did 175 miles to Bristol almost entirely on motorways without stopping thereby discharging the battery by about 85% in 3.5 hours. I did a slow charge over the weekend in Bristol back to 100% (and yes, I probably did unplug just as it hit 100%) followed by an almost identical 3.5 hour return trip.

I don't do many long trips like this and this is the first time in fairly cold weather. I have only rapid charged a couple of times in the last year so it's not that.

Anyway, it hasn't happened again - yet!
 
Your discharging whilst driving was at closer to 15kW so much slower than a Rapid charger. I'm surprised that it was so far out.
 
Geoffers said:
Battery balance seems like the most likely answer at the moment. This thought is stirring around in my little brain - if batteries require balancing as a result of rapid charging, would they not require the same as a result of rapid dis-charging? My thinking is this, I did 175 miles to Bristol almost entirely on motorways without stopping thereby discharging the battery by about 85% in 3.5 hours. I did a slow charge over the weekend in Bristol back to 100% (and yes, I probably did unplug just as it hit 100%) followed by an almost identical 3.5 hour return trip.

I don't do many long trips like this and this is the first time in fairly cold weather. I have only rapid charged a couple of times in the last year so it's not that.

Anyway, it hasn't happened again - yet!
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In theory the car should tell you when this is required. That's what the facelift manual says anyway. Only had mine a few months so have not seen this message yet.

Manual suggest you do it once a month but I would think this really depends on your use of rapid chargers and daily distance.
 
dragon2611 said:
If you have an OBD2 dongle carscanner may show min and max cell voltage. (Does on my pre facelift 5)

I think I paid about £12 for the Wi-Fi one that works with iOS, I had an older bluetooth one that worked ok with android but not ios (Was too old for bluetooth LE).
Click to expand...
Hi, I have been playing with an OBD2 reader and Carscanner and Torque lite.
Do you have any screen shots of the information on battery cells and SOH?
 
dragon2611 said:
If you have an OBD2 dongle carscanner may show min and max cell voltage. (Does on my pre facelift 5)

I think I paid about £12 for the Wi-Fi one that works with iOS, I had an older bluetooth one that worked ok with android but not ios (Was too old for bluetooth LE).
Click to expand...
I'd be interested in knowing the model of your OBD2 dongle. I'd like to see the cell voltages.
 
One year down the line and the mystery disappearing charge cropped up again, although I think I have worked out why.

The other day I completed a single 180 mile journey in miserable weather against a stong headwind and finished the journey with only a scary 7% charge left. It was late so I didn't get around to charging until the following morning by which time the charge had dropped to 2% and no miles on the GOM!

I then slow charged on a granny lead to 80% before heading out. Now I noticed the opposite effect. I travelled more than 10 miles before the battery dropped to 79%.

So, clearly the battery warms with use and extends the range - an effect probably only noticable in the winter.

The upshot of this is, don't assume you have enough charge to get to a public charger if you run very low and then leave the car in the cold!
 
While I agree the GOM will be affected by temp but the % of charge should stay fairly static.

It seems odd to me you would loose that much % over night.

I don’t drive my car for days at a time and % charge will not drop.

Then again I do not leave it sitting below 30% very often so may be an extremely low % behaves differently.
 
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