Ni-MH charging question...

Hi everyone. I bought a Panasonic BQ-390 charger with my Digital Camera earlier this year. It has 4 Panasonic AA's that are 1950 mAh. I am not having a problem with these batteries, but I found a different set of 5 Ni-MH's from an Audiovox FRS radio base station that I would also like charged. I thought they were lead-acid at first (why I don't know) but they are actually Ni-MH too. So my question is this: Can I charge these Audiovox batteries in the Panasonic Charger? They are only 1300 mAh, but I don't think that's a concern. I'm pretty sure all that matters is the output voltage of the charger, which is 1.5V DC @ 550 mA (it says "550mA x 4" on the charger, so this probably means that each battery is charged independently, making this a smart charger?).

Will I damage the charger or create a fire hazard? I had looked on the FRS radio's wall adapter to see its output voltage, but I forgot what it said.

Thank you!

If the cells are in a compatible form factor (AA, AAA, nipple, flat top, etc.) and your charger has four independent channels....then yes, it should work just fine. Of course, you'll have to charge two then three (or four then one) to get the whole packs' worth charged, but it would be better than a 'cooker' (dumb (oppose smart) current-limited charger). It sounds like your charger has 4 independent channels....are there four charge status indicators on it (one for each bay)?

There's only one status indicator that flashes while charging, and after approx. 2-4 hours its done. The panasonic batts get quite warm while charging, but I think the instructions say this is normal. They also claim not to charge any other brand or type, but I bet this is to make us believe that only their batts will work. (Hahaha?)

I'm not sure about it having 4 independent channels then.

You might be better off with using a charger like the Maha 401 or even a couple C. Crane chargers. You might be able to get away with one C. Crane if you can squeeze 5 cells in 4 bays...which is doable. /ubbthreads/images/graemlins/naughty.gif

The Maha 401 has four independent channels, whereas the C. Crane has one--it busses all the bays together in parallel, which works fine for sets of batteries, but I wouldn't want to put a fully charged pair in with a discharged pair. /ubbthreads/images/graemlins/icon15.gif This "feature" however would allow you to charge more than just four at a time (assuming you don't get up against the safety timer limit--probably not an issue with AA capacity cells).

Hey, I have another question (about discharging, etc.) I read the following on LedMuseum's website, and it got me concerned. I hope it's ok to quote:

"...to get the most power out of regular batteries, yet shut itself down before rechargeables become damaged. This level is around 0.9 volts per cell - when alkalines are considered "used up" and before rechargeables get damaged by overdischarge."

I learned a long time ago that batts develop a "memory", and that it was a good idea to drain rechargeable batts after they are considered "dead". My digicam stops working eventhough they are like 75% full. So I've been using a flashlight to drain them completely.

1) Is this completely wrong to do? I'll feel like an a** if it is.
2) Could I have damaged these "almost new" batts already if I've completely drained them multiple times?
3) Is it better if I just recharge them when the camera says they're low, or can it still develop a so-called "memory?" (The camera is really picky, cuz they still work fine in a flashlight)

Thanks.

The DME (Dreade Memory Effect) is a much-hyped phenomenon yet rarely encountered in normal practices. From what I understand it is also only an issue with NiCd cells, not NiMH or any other rechargeable chemistry. The consumer is far more likely to run into problems of voltage depression and soft shorts from constant cooking on so-called "dumb" trickle chargers. These are prolific in cordless telephones, cordless screwdrivers, ordinary rechargeable (the "plug-in" type) flashlights, handheld vacuums, etc.

In your scenereo I don't know why your digicam is not using the cells to their fullest extent. What brand/stated capacity/chemistry are these? NiCd and NiMH cells have a very low internal resistance compared to Alkalines, all the way to the very end--so your digicam, if designed to use rechargeables, should be draining them nearly empty. Is there a setting in the menu where you have to tell it if you're feeding it rechargeable cells versus disposable cells? This would switch the camera's internal discharge curve tables to match whatever chemistry you are using, so it can better predict how much life is remaining. Hope at least some of this helps! /ubbthreads/images/graemlins/smile.gif

What are the symptoms of voltage depression and what are the symptoms of memory effect? What goes wrong inside the cell to cause either of these?

I have a Panasonic BQ-390 rechargeable battery kit. (4 AA's rated at 1950 mAh, one 4 "channel?" charger.

Camera: Kodak EasyShare DX 4330. Can't see any setting for battery type, etc. I've heard somewhere that these cameras are really picky for voltage. It'll work for a while when the low batt icon comes up, but not for long. It'll just die a short time later. I have learned that not using the LCD preview screen saves a LOT of battery life. Also, I loved the performance of the CRV3 lithium batt that it came with. I got like 100 pics or more with it.

See ya

Hello CanadianGuy,

It is my understanding that all re-chargeable batteries can show the memory effect if they are subjected to EXACTLY the same discharge and charge cycle. This effect is more noticeable in Ni-Cd batteries, but Ni-Mh batteries can be made to demonstrate the memory effect as well.

For example: If you take 10 pictures with your camera (using exactly the same settings) then recharge the batteries overnight and do this every day for a year, you will have conditioned your batteries to supply 10 pictures worth of energy.

Re-chargeable batteries rate the number of cycles they can utilize. It is my understanding that deeply discharging uses up full cycles, where a partial discharge followed by a charge uses less than a full cycle. I believe the batteries will last longer if you just top them up from time to time. Ni-Mh's require a few cycles to get to maximum capacity and may benefit from a full discharge a few times when you first get them. After that, just top them up from time to time.

Tom

A very good explanation (as well as other things) regarding DME is available on Anton Bauer's Video Handbook, Voltage section. Scroll down a bit and they'll even show a sample time vs. voltage graph. This is specifically for NiCd cells, however.