Anything's possible

[Commander Kinsey]

Gas is produced when the chemicals are old, tired, and converting into something else?

[invalid unparseable]

That 10mA will do damage to the battery over time. It won't go into the battery and vanish without doing anything. Modern cellphones have very elaborate charging circuits to keep the battery fit. Idiotic engineers who did what you do have caused spontaneous combustion in motorized skateboard fires and airline seatback entertainment unit fires.

All the lithium batteries for my gadgets have protection circuits that would totally disconnect when the battery is fully charged. I know the charger is totally disconnected because after a few days the battery will return to its nominal voltage instead of peak voltage while still connected to the charger. I have to disconnect the charger and then reconnect the charger to get the circuit to restart charging the battery again.

The elaborate charging circuit in modern cellphones is the reason I can keep my cellphones constantly connected to the 5V USB voltage source and I have never had swollen cellphone batteries like in the old days.

[Commander Kinsey]

0.01A x 4.2V = 0.042W. Not sounding like anything to cause damage.

In fact I regularly charge 18650 cells from a cheap shit 99p Chinese charger, and by the time it's turned off, the battery is far warmer than body temperature, yet it hasn't broken the batteries.

Who charges their skateboard forever?

And so should any battery with such a shit chemistry.

Nominal does not equal peak? If I take a battery off the 4.2V charge and put it in a drawer for a week, it still reads 4.2V. 3.7V is empty, 4.2V is full, and linearly inbetween, very easy to tell how full it is.

Unlike Lead Acid where charging is 13.8V but full is 12.7V.

[Commander Kinsey]

Why do you need an elaborate circuit? Stick 4.2V with current limiter on battery. When current drops to x mA, switch off. Hardly elaborate. They've had such stop circuits on NiCad and NiMH chargers for ages, the ones which charge in 2-5 hours, they didn't bother on the 16 hour ones. Now those were elaborate, as Nickel batteries do weird shit, their voltage actually drops when they get full. You need some kind of voltage change detector.

When I was a kid I super fast charged a 7.2V NiCad radio controlled car pack in the front seat of my dad's Volvo when we were camping, off the cigarette lighter. I forgot the time (I meant to leave it on for only 6 minutes) and went off to the loos, then came back to rather angry parents and white powder all over the seats. Surprisingly, apart from that pack, doing this from either a 12V car battery, or the mains with a transformer, never damaged any batteries. I just timed it to a bit less than when the battery got hot. Very handy when a group of us were out with many cars and the batteries didn't last so long. We used them at the local park, broke into an outside toilet with a light, and gerry rigged the charger into the light socket.

[invalid unparseable]

One year is: 24 hr x 365 = 8,760 hr.

0.042W x 8,700 hr = 367.92 Watt-hour.

That is equivalent to pumping 367.92W of excess energy for an hour into the battery.

I don't think I should continue wasting my time trying to make sense with you.

[FromTheRafters]

For some values of "equivalence" this is true. In the sense that a 1000 amp-hour battery could actually withstand 1000 amps for an hour without the heat factor figuring in. Heat and high temperatures tend to kill batteries.

[invalid unparseable]

The excess charging current going into the battery will definitely do something. You don't see the damage in a few days and think it will be OK in the long run. It is not true. In lead-acid batteries, the excess charging current tend to simply slowly "boil off" the water through electrolysis. In lithium batteries where there is no liquid electrolyte, the excess energy will do permanent damage to the lithium components. Apparently bulging is a direct result of that. It is simply idiotic to insist connecting a constant voltage for extended period of time to the battery will do no harm. That is the same reason idiotic manufacturers made lithium battery powered devices that would catch fire for no good reason.

Listen. It is definitely true that all the OEM chargers for my lithium batteries would completely turn off when they detect the battery is fully charged. Apparently the decline in science and technology in Britain since WWII is because it has acquired a moronic population, maybe due to importing too many (dumb-blonde?) war-brides from Holland.

[nib]

What I don't understand is: if you connect a power source at exactly V volts to a battery with a fully-charged open circuit voltage of V why should any current flow once the battery is fully charged? No potential difference, no current.

(Isn't that how cars work? They have a voltage source that's temperature- compensated to exactly equal the battery's fully charged voltage. They certainly don't use timers or computer models of charge in and out, or measure specific gravity of the electrolyte!)

nib

[FromTheRafters]

nib submitted this idea :

Local Action. A type of self-discharge.

[nib]

So if it's "self-discharge", why doesn't the current exactly balance it? I can't see how current can flow with no potential difference, it seems on the face of it to disobey Ohm's Law!

nib

[invalid unparseable]

Ohm's law does not apply inside a battery's electrochemical process. The theoretical "internal resistance" of a battery is merely an imperial number for mathematical calculation only, and the theoretical internal resistance of a battery changes constantly in the same battery.

It is not a simple "resistive load" inside a battery. It is an electrochemical process inside a battery. The energy you put into the battery will do work. If you put excess charging into it, the energy will do damage to the battery.

A normal battery will stabilize to its natural "nominal voltage" at rest. A battery will rise above its nominal voltage when charged. That means if you put any voltage above its nominal voltage, some current will go in and induce a terminal voltage to oppose this charging voltage through an electrochemical process. That means some current is constantly going into the battery to produce the extra voltage above its nominal voltage to oppose the charging voltage. This incoming energy will slowly boil off the water (H2O) into H2 and O2, and cause bulging or crack the casing if there is no vent. In the case of lithium battery where there is no liquid electrolyte, the excess energy input into the battery will cause bulging in the lithium chemical components, which are soft putty in texture.

Don't assume there is no current going into a 12V car battery if you permanently connect a 13.8V to it. The nominal voltage of a 12V car battery is about 12.7V. Therefore some electrochemical process will have to take place inside the car battery to created that 13.8V at the battery terminals to oppose the incoming 13.8V.

[nib]

But what we said was, connect a battery with open-circuit voltage V to a source voltage V. There is no voltage difference over the connecting wire. There is therefore no current. Nothing at all about the internals of the battery?

nib

[invalid unparseable]

You apparently believe in magic and fairies. If the source voltage is higher than the open-circuit voltage of the battery. common sense will tell you that the voltage of the battery will rise up to try to equalize the source voltage. Where do you think the extra voltage in the battery comes from? It comes from drawing electric current from the source voltage to cause electrochemical process inside the battery. Therefore, there will always be electrochemical process inside the battery as long as the source voltage is higher than the open-circuit voltage (nominal voltage) of the battery.

[nib]

Did you read what I said!

I did not say "If the source voltage is higher than the open-circuit voltage of the battery"

I said it was EQUAL !!!

nib

[invalid unparseable]

My bad. Sorry.

The nominal voltage of a car battery is a manifestation of the internal chemistry inside the battery. It is changing continuously according to the environmental factors like temperature and pressure. There is no way you can connect an external voltage to it that's  EXACTLY  the same voltage as the nominal voltage of the battery. Current will either flow into the battery from the source if the source voltage is slightly higher, or the battery will discharge into the source if the source voltage is slightly lower, unless the source has a rectifier to prevent reverse current flowing into the source. But the whole thing is a meaningless exercise.

[nib]

Thank you, we arrive. So if the voltages are equal the current is zero. Ohm's Law is safe.

As an aside, I notice that that car voltage regulators are carefully temperature compensated.

nib

[invalid unparseable]

You can never get the two voltages exactly the same before connection. Any minute voltage difference before connection will cause current to flow in one direction or the other after connection. Ohm's Law doesn't apply here because how much current will flow has nothing to do with Ohm's Law.

I don't see the necessity of temperature compensation in dealing with car batteries. Car batteries are constantly in a charge-discharge cycle. There is no point to be exact. Just make sure not to overcharge and boil the battery fluid off.

[Rod Speed]

Nope, the car turns the charging off when the battery is fully charged.

Nope.

They actually measure when the battery is fully charged.

Correct.

[Rod Speed]

But you can certainly adjust the external voltage after connection so that no current flows in either direction.

That is needed to determine when the battery is fully charged so you can stop charing it so the battery isnt destroyed eventually.

Not on a longer trip once the battery is fully charged.

But you need to compensate for the temperature to do that.

[FromTheRafters]

Circular superconductors also have current without EMF voltage, but that's not relevant here in lead/acid batteries. Ohm's Law as it was originally formulated is like the law about coming to a full stop at stopsigns and often gets ignored. It's really about the middle ground and not the extremes.