Even though bad, a battery would still have intenral resistance. Note a capacitor can suffer a failure of the insualtion between the "plates," such as from a high surge.
A bad battery has a very high internal resistance as a rule. When you measure the charging current of a bad battery, it's very small right from the start.
Here is my take on the battery versus BCR issues. First the battery. The MTH 8.4V battery is 2 4.2V disc. Other manufactures may use 7 1.2V cells (smaller then AAA). Usually the 8.4V battery last around 4-5 years. They are normally rated at about 120-150maH. Makes sense, since the cells are smaller and have to provide higher voltage.
The 2.4V batteries are 2 AA batteries and rated at 700maH. Quite more energy available since the cells are larger and the provided voltage is lower. They normally last 7 years. I had one in a cordless home phone that was over 10 years old and still worked fine.
The PS-2 3V boards are less prone to failures, and respond fine with older batteries. In my opinion given the type of 2.4V battery and the board set, BCR don't really make much sense for PS-2 3V.
For the 8.4V battery the potential for it to get to a low enough state that the voltage isn't sufficient to operate the electronic board is certainly higher then a 2.4V battery.
As far as the electronics, the early PS-1 boards supposedly were not rated to provide the ma necessary to charge the BCR. This comes from QSI. Later boards were modified to beef up those components. Which components I don't know. Could have been the 24ohm resistor, maybe a board trace that was too thin. Most of the PS-1 components where through hole, and a FET is used to turn off the battery after a RC circuit times out.
PS-2 5V used a 5V processor and most of the microcontrollers are 5V. I assume the battery voltage is converted down via a buck circuit. I know that the Voltage regulator was operated near its limit, and some sound profiles were written to reduce the volume (load on the VR) until certain processes were completed. The PS-2 5V certainly can have its share of undetermined failures (shorted diodes, bulging capacitors, or just plain dead).
As mentioned, I have seen shorted 8.4V batteries come out of PS-2 5V engines that were dead.
I do believe the PS-2 3V is charged via a FET and processor controlled. One concern I would have with slowing the charge rate, is the engine is non responsive when the voltage at the battery terminal is too low, and the volume is reduced. Is this an overload on the VR, processor, or other components on the board?? Don't know. Seems like folks are using them fine. I just don't know how some one can alter the charge rate, and know the effect on the circuit board, without a full understanding of how the board charges the battery or BCR.
I guess seeing how the board reacts to a BCR makes me hesitant, because even a weak battery doesn't force the board to go into a protect mode like it does everytime a BCR has to recharge.
I have seen PS-2 3V boards that provide power for shutdown, but don't charge the battery. I have seen failures where there is no shutdown power available. The 3V boards use a 5V regulator for the microcontrollers and a 3.3V regulator for the 3V processors. The 2.4V battery is boosted via an inductor to get 5VDC for the shutdown when no AC power available to drive the 5V regulator, which also powers the 3.3V regulator.
So my conclusions on use are that I can see them for the PS-1 and PS-2 5V primarily because the batteries don't last as long and some early stuff doesn't have charge ports.
For PS-2 3V I think they are not necessary because of the life of the battery, charge port, and robustness of the boards even with bad batteries.
No conclusions here on failures, just some more info. Recently became a Dodge guy after a few years as a Chevy person:-) So take it for what it is worth.
G
Originally Posted by GGG:
... I just don't know how some one can alter the charge rate, and know the effect on the circuit board, without a full understanding of how the board charges the battery or BCR.
That's what I call hitting the nail on the head.
You will see battery charging specs such as C/10 which is the charging current of 1/10th the capacity...so, for example, charging a 100mA-Hr battery at 10 mA (for 10 Hours). So IF the battery charger controls the charging current, then you can't limit the current with a series resistor. Of course if the resistor is large enough you can limit current by starving the voltage. But this can be a tricky game to play since the voltage response at the terminals of a rechargeable battery vs. a super-capacitor are dramatically different when supplied with a constant current.
