What is normal

C

Cliff Mitchell

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Wyee Point, NSW, 2259 Australia
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MG ZS EV
I have now had the MG for over three months. For most of that time my 12 volt battery remained steady at 14 volts - start the vehicle 14 volts, drive the vehicle 14 volts. Recently I have noticed that the battery reading is down to 13 volts when I start the vehicle and it does not rise to 14 volts until I have travelled about 5 kilometers.

Is this an indicator of impending doom or is it normal?
 
I can't say I've monitored my 12v battery that closely, other than the bars on the dash. The 12v battery gets its charge from the HV battery, so I would say what you've posted about the 5k increase isn't worrying (to me, at least). As I'm sure you know, using accessories like the radio with the cat not in ready mode, can discharge the 12v battery quickly.

No doubt someone more clued up than me will reply soon.
 
Driving the car makes no difference. If your HV battery is engaged it charges the 12v. Sometimes it takes a little while to get there. Unless you’re getting consistently very low 12v readings it sounds normal.
 
It usually comes up to 14v within a minute or so unless you have a load on like lights, HVAC etc.
I would be tempted to put the battery on charge, preferably on a battery conditioner like the CTek chargers, to boost it up and see how it goes.
 
When you see 14V you are looking at the charging voltage not the battery voltage.
If it's a little lower than 14V that most likely means the battery is already at a good state of charge and doesn't need to be floated at quite so high a rate.
 
Cliff Mitchell said:
I have now had the MG for over three months. For most of that time my 12 volt battery remained steady at 14 volts - start the vehicle 14 volts, drive the vehicle 14 volts. Recently I have noticed that the battery reading is down to 13 volts when I start the vehicle and it does not rise to 14 volts until I have travelled about 5 kilometers.

Is this an indicator of impending doom or is it normal?
Click to expand...
NO - is the simple answer Cliff.
I have witnessed this sometimes lower reading of below 14 volts on my ZS EV as well.
On the ZS it is USUAL to see the two white bars above the central position on the battery gauge displayed when the car is in the fully ready status.
Although, on more than a few occasions I have witnessed the display only showing one single light bar shown above the central position, suggesting that the 12 volt status is a little low.
But the battery status display will have increase after only travelling a few miles.
What I have also found, is when travelling at night time, with a lot of 12 volt demand being consumed ( wipers / head lights etc ) the 12 volt battery gauge is showing the lower status for a long time when travelling.
But when arriving home, as soon as the head lights etc are turned off, the battery gauge returns to straight to the higher status.
I do not believe the 12 volt battery is running flat, it is just the increased load being reported on the 12 volt gauge.
I do have a 12 volt smart battery charger and I have offered in to the battery on a couple of occasions, just to see if it accepts a long charge ?.
This may indicate if the battery was indeed low, before placing the car on charge.
But after only being on charge for less than 1 hour, the battery returns a fully charged condition.
Therefore the 12 volt battery was almost fully charged before the charging commenced anyway !.
 
Joe said:
When you see 14V you are looking at the charging voltage not the battery voltage.
If it's a little lower than 14V that most likely means the battery is already at a good state of charge and doesn't need to be floated at quite so high a rate.
Click to expand...
If I for example complete a long run (say 2 hours) my 12v continually reads 14v. Or of I sit in the car in ready for an hour it always reads 14v. In fact when it does show slightly less (usually after an initial start) it always very quickly returns to show 14v.When the HV pack is engaged it will always show 14v after a short time. The 12v showing less than 14v is when the HV pack is disengaged and the 12v battery voltage is shown - not the charging voltage.
 
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Joe said:
When you see 14V you are looking at the charging voltage not the battery voltage.
If it's a little lower than 14V that most likely means the battery is already at a good state of charge and doesn't need to be floated at quite so high a rate.
Click to expand...
But the handbook says it's the battery voltage.

Edit: see screenshot
1625781863609.png
 
Last edited:
rbpasapera said:
But the handbook says it's the battery voltage.
Click to expand...
Yes, it is the battery voltage, but it's forced higher by the charging current. You will never see 14V or more when not being charged, except for a few seconds after charging stops.

So 14.x volts isn't indicative of the state of the battery, it just means it's getting charged. Our auxiliary battery "voltmeter" with one volt resolution (I call them bricks) is pretty useless, unless something drastic happens to the battery. I'd prefer a digital display with 0.1V resolution, or use that instrumentation space for something else.

Edit: but I guess it's better than just a warning light.
 
I guess you could get a more realistic actual battery voltage reading in Accessory mode with everything switched off.
 
Lead acid batteries fully charged are 13.7v. If the charging voltage is only 14v this is lower than most alternator systems and that could explain why you see only 13v on occasion . Ie, the charge system is a bit marginal on charging voltage.
 
Tim Green said:
Lead acid batteries fully charged are 13.7v.
Click to expand...
No, more like 12.7V rested, occasionally up to 12.9V (depending on temperature). It can take half an hour or so for the voltage to fall below 13.0V after a charge. But over 13.0V on a 6 cell lead acid battery is not sustainable.

Float charge voltages are generally 13.5-13.8V, where the battery (if not full) will actually still charge, but very slowly. I'll agree that only ever float charging the auxiliary battery during main battery charging is a bit marginal.
 
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