12v battery maintenance, issues, etc.

[r44flyer]

40 minutes ago, hind said:

The thing is, it will not charge it to 100%, by design. You can charge the battery to 12.7V, drive a car for 100 miles, let it rest and after 30 minutes you will read 12.5V. Meaning that this drive effectively discharged your battery. This is the issue with relying on the car. 

As an electronics engineer with much experience in charging batteries, I respectfully don't agree.

Charging a Battery requires a voltage higher than the normal state of the Battery to charge it.
Normally you would charge a 12V lead acid Battery at 2.25V per cell i.e. a 13.5V to 13.8V charge voltage would be considered a normal range.

When the charging voltage is removed the battery will then settle to it's normal state, typically 12.5V to 12.7V.
This is called sag. However, it doesn't mean the battery is not charged to 100%, when in fact it may well be.
That lower voltage is considered the battery's normal steady state voltage when fully charged, governed its' chemical construction, temperature etc.

If systems are connected to the battery, which they are of course even when the car is off, a small discharge current will still occur, and further reduce the battery steady state voltage slightly.
How long it takes to fully discharge a battery in good condition is then decided by the quiescent discharge current.

A battery in poor condition may settle to a lower state, and might even appear normal around 12.0V to 12.5V (our rubbish battery measured 12.5V off load), but it will not have any capacity left.

So a reasonably long journey around town will always fully charge the 12V battery.
Hence why I have never had to boost ours with a mains charger in 9 months since it was replaced.

[Dala]

21 minutes ago, r44flyer said:

...So a reasonably long journey around town will always fully charge the 12V battery....

[r44flyer]

42 minutes ago, Dala said:

Context is everything so I'll play along anyway...
Assuming this is a monitored 12V Battery on a car and the X axis is hours.
I don't know how old the Battery is, don't know the state of the Battery capacity before hour 0 so I've no idea whether it had been on charge/driven/or how long before hour 0.

All we can see is that at hour 0 the battery was around 12.7V and was settling to a steady state of 12.43V by hour 7, assisted by a small quiescent discharge current by the car's 12V systems.

Just after hour 7 the car was driven/charged for just over 1 hour during which a charge voltage was applied.

From hour 9 to 21 the battery settled back to its steady state around 12.4V
The quiescent discharge current would have resumed and the battery stayed at a steady state, albeit with some percentage loss of capacity up to hour 21.
The flat line indicates that the 12V battery was reasonably charged, but this graph cannot reveal at what capacity.
You would have to do a discharge test down to the correct voltage to prove what capacity the battery actually had left, which in this case could easily be anywhere from 20% to 95%, depending on the state of charge, battery condition and temperature. So the graph doesn't actually prove anything for me.

I'm not saying that a 1 hour journey will fully charge a flat battery, I'm saying a reasonable journey, yes 1 hour would do, will top up a good battery, and replace a fair proportion of its capacity since its previous use. 

My original point that the 12V battery is being charged every time the car is driven stands, evidenced by the fact that my replacement Yuasa battery has not been charged in any other way since January.

[Dala]

5 hours ago, r44flyer said:

...Just after hour 7 the car was driven/charged for just over 1 hour during which a charge voltage was applied...

12.8V is not "charge" but "maintenance" voltage

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the day before

How the system evaluates charging and maintaining the car Battery by driving is still a mystery to me.

[hind]

8 hours ago, r44flyer said:

As an electronics engineer with much experience in charging batteries, I respectfully don't agree.

With charging lead acid batteries? If yes then you will know that the Battery capacity is linked with the electrolyte density. And you increase it with charging, but it takes time. The higher the voltage the faster the process, but above some point the electrolysis process becomes more intensive, turning water part of the solution into hydrogen and oxygen. That's why you rarely charge the Battery with the voltages higher than 14.4V. With the Battery out of the car you can crank the voltage to 16V, keep it like that for a few hours, refill with demineralised water and you are good to go. But with the battery inside the car you can't do that easily, so you have to rely on the absorption phase of the charging, which is based on keeping the voltage on the maximum safe level and letting the battery to rebuild the electrolyte density and it's capacity. 

But for some reason the charging algorithm in Yaris doesn't always use maximum voltage, dropping it to 12.7V. Could you imagine what's the charging current then? How long would it take to not only charge it but restore the correct electrolyte density? In no way you can restore what's lost during parking. And because of that to keep the battery in a good shape, regardless of the manufacturer, in Toyota Yaris IV you need to charge it manually from time to time. Otherwise it will degrade over time and fail sooner than it should 

[HarryW2024]

I do wonder what the charging algorithm is as used by Toyota. It’s not as if it’s constrained by the simple constant constant voltage (CV) charging of an alternator system of a normal car. Ergo it should allow for phase charging which is a combination of Constant Current (CC) and CV as it swtiches between Bulk, Absorbsion and Float phases.
Also being a Calcium Battery (Ca/Ca) it has to manage sulfation of the terminals/plates, which the type is particularly prone to, giving a false voltage level readout due to surface charging at too low levels and hence not actually fully charging it.