Is this normal?

[chrome-addict]

I just ran a set of fairly fresh Sanyo 2700 mAh AA's in my Cannon Powershot A80 until the camera shut itself off. I pulled the batteries out and they showed inconsistent voltage readings across the board. The batteries read 1.25v, 1.09v, 1.08v, and 1.14v. Thinking that I had some faulty cells, I reloaded the camera with some older, but good, Energizer 2500 mAh cells and used them until the cameras battery warning light came on. I pulled them out, measured them, and got similar inconsistent readings ...is this normal?

I usually like to run my batteries down to the same level before recharging them, because I believe it keeps their capacities consistent. Is this really the case, or does it really not matter? If it does, this camera is going to drive me BONKOS!!

 

[LuxLuthor]

Voltage differences tend to be greatest at the end of their run time, but these may be also self discharging at different rates.

What I would do is check the voltages at various intervals while using to get an idea at what point they start separating. I would not be worried if the separation of readings was at the tail end.

 

[cerbie]

Each cell will have a little different capacity and a little different resting and load voltage, and different capacities. If the batteries are run in series (as is likely), these will be most pronounced. Also, if the camera is designed with NIMH in mind, it will have a fairly high cut-off voltage (4.5v, by the looks of it). You don't want to drain multiple NIMHs in series dry, so it should cut off around 1.20v under a light load, so as not to have too great a risk of reverse-charging.

The short answer: this is perfectly normal. As always, try to keep the set charged and discharged together, and if they've sat for more than a couple of weeks, try topping them off before use (this shouldn't be a concern for devices that use only one cell).

 

[SilverFox]

Hello Chrome-addict,

Your question about running the batteries down to the same level each time may be answered in this thread.

It looks like you may have one strong cell in your pack. Your camera is probably set to shut off at 4 volts under load. Let's assume that all of the cells drop evenly, even though we know that is not the case. If the camera shuts off at 4 volts, each cell would have to drop 0.14 volts under load to get the pack to read 4 volts. If you do the math you see that none of your cells are being driven to very low voltage levels, so everything is working well.

The next question involves charging. If you charge on an independent channel charger, all is fine and you just have one cell that is slightly better than the others. If you charge in pairs, your cells may be out of balance with each other and that could be causing some of the imbalance you see.

As LuxLuthor pointed out, voltage imbalance is usually greatest when the cells are in a discharged state. When you charge your cells, let them rest for 30 minutes and check their voltage then. If there is an imbalance with fully charged cells, you may be seeing some cells that are developing voltage depression.

Tom