Wow, so the voltage charging peak is roughly the same as the battery output?

The charger output is a constant current, not a constant voltage since both cannot occur at the same time.
Since the charging current is constant then the amount of battery charge controls the charging voltage including the voltage peak.

 

NiCd and NiMH rechargeable batteries are charged at constant current. That is why you need to adjust for current from a constant current power supply.

An ideal constant current source has infinite source resistance.

By adding a resistor in series with a constant voltage bench power supply you are adding external source resistance. The higher you make the resistor value the closer you approach the performance of an ideal constant current source.

If the charging current is 1A and the series resistor is 100Ω, the power supply voltage would have to be set to (100V + battery voltage).
If the charging current is 250mA and the series resistor is 100Ω, the power supply voltage would have to be set to (25V + battery voltage).

The effect is that when the battery voltage increases from 0.8V to 1.4V while being charged there will be little change in the charging current.
Another way of putting this, if you set the power supply output voltage to 25V instead of 26V the charging current of approx. 250mA will drop by 10mA or 4% which is nothing to worry about.

 

hi ram,
Consider the current requirement of the device being powered.
Can the 0.8V battery output enough current to help power the load device.?
E

No, my point was not why the device is not working, my point was how is it possible that in a 3 parallel AA battery configuration for a given device, you end up in a situation with x2 batteries 1.2V and one 0.8V. According to what I've read, the 3 batteries should always have the same V because when one is going down faster, the other 2 recharge it until equilibrium.

 

No, my point was not why the device is not working, my point was how is it possible that in a 3 parallel AA battery configuration for a given device, you end up in a situation with x2 batteries 1.2V and one 0.8V. According to what I've read, the 3 batteries should always have the same V because when one is going down faster, the other 2 recharge it until equilibrium.

It is possible that when the cells are disconnected and measured the one showing 0.8V is dead and needs to be replaced.

 

Oh boy, hahaha, I think I got it.

1) So if a battery is charged and you use it, you connect it to a light bulb and the current goes from POSITIVE to bulb (resistor) to NEGATIVE. If you close the circle, inside the battery the current is going from NEGATIVE to POSITIVE, right?

2) When you charge it, when you put POSITIVE from power supply to POSITIVE from battery, and NEGATIVE from power supply to NEGATIVE of battery, which seems like nothing is reversed, actually, IT IS!
Because that way the power supply (ps) will make current inside battery (b) go from POSITIVE to NEGATIVE, which is the opposite of situation 1).

Am I right?

Which would mean connecting +ps to -b and -ps to +b, you would be forcing externally to flow current inside battery even more harder than situation 1), correct?

Yaakov made me click!

 

Slightly higher, yes.
Why is that surprising?
That's not possible.
The batteries must be in series, not parallel.

Surprising because I expected a higher voltage to undo the process, something like 4V or 5V or more. The undo processes always ask for higher pay.

May be you are right, it could be that all the devices that have more than one battery are all in series?
I mean house hold devices...

But if something works @1.5V but you want it to lasts a lot of time, you would connect in parallel 6 battery pack, right?

 

But if something works @1.5V but you want it to lasts a lot of time, you would connect

More likely, you would use a larger cell. A D cell is equivalent in capacity to about 6 AA cells.

Most devices you will find with multiple cells have them in series.

Bob