Batteries, Memory effect and Voltage depression

[Replicon]

Hey,

I was reading the manual on my digital camera (sweet sony dsc-p52), and they were saying it's best to use up all your batteries before recharging, to avoid memory effect. I recall this being an issue with an old camcorder we had: If you recharge the battery before it mostly expires, it whines about expiring really soon (close to the point where it was when you started recharging).

Now, according to Dan's data, it looks like this is called voltage depression. Anyway, my digicam takes AA NiMH rechargable batteries. How much should I let them drain before recharging? Should I wait till the camera says they're just about out, or is it safe to recharge them earlier, like when it's indicated as low. Suppose I keep recharging it when it's half empty... will that have any effects? Like if I do that 2-3 times, will I notice the low battery notice appearing earlier than it should?

Oh yeah, other battery question: Why is it (on my MD player anyway) that when your battery says low, and then you turn the device off for the night or whatever, when you start using it the next day, the battery indicator is high to medium for a long time? I'm thinking there's some discharging that needs to be done, which adds to the voltage, this skewing the sensor results, but is that all there is to it?

Thanks,
Raplicon

 

[0roo0roo]

mem effect as dan says is buncha bull for the most part. and any extra life you get from doing all sorts of tricks that waste time are going to save you nearly nothing, and waste your time. so what if your batteries go capput after 480 charges instead of 500... charge as needed, its much worse to not have a battery charged when you need it.

 

[uart]

Anyway, my digicam takes AA NiMH rechargable batteries. How much should I let them drain before recharging?

NiMH batteries do not suffer from memory effect to the same extent as the older NiCd types. It should be safe to recharge your batteries from any given initial state. One thing that I like to do (just to be sure) is to try and "mix it up" a bit by not always starting the charge at the same point. That is, sometimes I will let them run right down, sometimes I will charge them from half way, basically whatever is convienient for me on the day.

Oh yeah, other battery question: Why is it (on my MD player anyway) that when your battery says low, and then you turn the device off for the night or whatever, when you start using it the next day, the battery indicator is high to medium for a long time?

As a battery is used the electrolyte becomes chemically depleted, this is basically what a "flat" battery means. Now this depletion first occurs near the electrode surface, as this is where the chemical reaction is taking place. So the electrolyte near the electrode is chemically "flat" but electrolyte deeper within the cell may still be in good condition.

Under slow discharge then the "good" electrolyte will gradulally diffuse in toward the electrodes and the whole cell will more or less discharge uniformly. Under more rapid discharge however the diffusion often cant "keep up" and so the battery appears to be flat due to the localized electrolyte depletion near the electrodes. Now if the cell is left to sit unused for a period of time the good condition electrolyte has time to diffuse thoughout the cell, in particular toward the electrodes, making it appear that the cell has somehow spontaniously recharged itself.

 

[Replicon]

Ah, thanks, that makes sense

 

[Yossarian451]

For my NiMH I always run them down all the way the first time. After that I use and recharge as needed.

 

[Mday]

just be sure to keep the same "batch" of batteries together. you may want to label your battery sets.