Warning! after5pm.net batteries SUCK!

As far as I know, the charger determines whether to charge the battery or not strictly by measuring the voltage of the battery (under a load maybe). There are surprisingly sophisticated charging algorithms working inside those "simple-looking" devices.

The real test is how many of the same kind of batteries from After5pm are not working correctly. If there are enough of those then you can claim they suck. I have some from there as well but as yet have not put them to the test.
I will start out with them in my 20D at my next wedding (two weeks) and post the results if I have any problems. So far I have been able to shoot an entire wedding on the two batteries in the battery grip - with one showing it still had a full charge!


Lou

Charger measures the amount of amps it takes to push the voltage through the batter. This is the resistance to the current.

When a battery becomes fully charged the amps needed to push the voltage through the battery goes down. The resistence is less.

When a battery is shorted there is no resistence. So the charger would need very small amount of amps to push the voltage through. So the charger thinks the batter is charged.

A bad battery would need very low amps to push the voltage through the battery. Again the charger would think the battery was charged when it was not.

I'm not trying to explain why a battery goes bad just why a charger would think the battery was charged when it was not.

Steven, I think you have your electronics turned around. Current flows, not voltage. This "pushing the voltage" stuff is hooey.

---Bob Gross---

The term is electron flow and engineers believe it is from neg to pos. batteries usually short because the internal plates touch together not allowing the chemical reaction to take place and make voltage.I do not like to use the word short becouse it is a reference to gnd and that is not happening.

No, the term "short" is not a reference to ground. "Short" is simply a term for when two voltage nodes have a fault connecting them, and it might be a hard short (zero ohms) or it might be a slow short (abnormally low ohms).

Batteries can go bad for multiple reasons. If internal cells go into a shorted condition, then you may loose a major portion of the open circuit terminal voltage. In other words, the 8 volt battery suddenly becomes 4, or something like that. Lithiums don't go this way very often. A common battery failure point is if internal resistance increases. Normally internal resistance builds up slowly over its life. Since current flowing out of the battery passes this resistance, power is lost. If the internal resistance builds up too much, then the battery will look poor. Its open circuit terminal voltage (like with a voltmeter) will look relatively normal, but that is because there isn't much current passing the internal resistance, so there isn't much power loss, so it looks relatively normal. But when you drop a load on it, the increased current passing the internal resistance causes the battery's effective power delivery to look really bad. In other words, the camera might show a low battery icon even when the battery is fresh out of the charger. Or, worse yet, the camera might not even start up successfully, and it might not have enough delivered power to light up the icon to show a flat battery.

What I guess is that a Canon charger might sense current flow into the battery that it is charging. If the battery is 7 volts open circuit, then the charger pumps a certain amount of current into it until the battery comes up to 8 or 8.5 volts. At that time, it can't pump any more, so the charging current goes to zero. Then the charger indicates "steady LED" which means that (it thinks) the battery is full. If some battery fault (such as very high internal resistance) was present, then the charger could not pump any current into it, and the charger might show "steady LED" even though the battery isn't much good. In other words, if the battery was "high resistance", it might show this way, and that is certainly not the same as "shorted", but it might seem this way.

I think that the only practical way to get a good measurement on a battery is to measure its terminal voltage with some nominal load present. Most of the time, we shouldn't have to go to this trouble. Industrial users of batteries do it some. The battery icon on the camera measures with a nominal load present.

The question that we have not addressed is this: What makes a relatively new battery suddenly go high resistance? If it were overcharged, I could understand it, but most of the Canon chargers are intelligent enough to taper off the charge current when a certain point is reached. If the battery had been abused, cooked, frozen, or otherwise stepped upon, I could believe that, but I doubt if the users here do that to their batteries. If there had been a fault in the camera system, like with an I.S. lens that is constantly working, or with an autofocus motor that is running constantly, then I could understand it a little.

Maybe it is just that one out of a hundred batteries that suddenly goes bad.

---Bob Gross---

I still don’t like the word short so let’s call it by its full name short circuit and it occurs when current takes an accidental path short of its intended circuit. It thus does not flow in its normal circuit and serve the connected load. Short circuits often involve the regular circuit conductors and are caused by the creation of a path of lower resistance than that of the normal circuit.

If you would please describe what a node is. I have heard this tern in reference to communication systems but not voltage sources?

NiMH batteries or Nichol metal hydride produce about 1.2 to 1.3 volts so to achieve the desired voltage and amperage you will have to create a series and parallel circuit with the cells. If any of the cells in the series part of the circuit failed there would be a voltage drop like you described.

The other great killer of battery is vibration or the current regulation card in the battery is very cheap. Back to that old adage you get what you pay for.

Sorry for all the non Photography discussion Robert and I are probably boring all of you.

I don't think it is within the scope of this forum to go into basic DC circuit theory. A circuit node is the same as a systems node. A DC voltage can be measured at any node of a circuit, and DC current can be measured flowing in any link of a circuit. Links connect nodes.

Do a web search on Kirchoff's Laws.

---Bob Gross---