Preserving/Reforming NiMH Batteries

[CoolToolGuy]

I have a digital photo frame that can be powered by AA batteries, and the manufacturer specifies NiMH batteries. The frame sits in my desk drawer most of the time. I got it out to take with me to Thanksgiving with the family to pass around and show some images, and the batteries were dead flat. I tried charging them, but the first attempt only gave me about 45 seconds, so I plugged it back in for about 16 hours and got about 2 minutes. By then it was too late, and I took one of my other frames that must be plugged in.

I have several questions:
-What is the best way to keep NiMH batteries at top charge? Would it hurt to keep the unit plugged in and charging all the time?

-It seems that, even from a flat battery, a charge/drain/charge process restores the batteries. With the latest charge I get 15 minutes out of them. Should I just keep this up? NiMH batteries aren't cheap, and I don't want to buy a new set every time I want to use this frame.

-Could I switch to Alkaline batteries? I know I can't recharge them, but it may be cheaper in the long run.

-Why would the manufacturer specify NiMH?

Thanks in advance.

Have Fun,

[Cadwell]

Are you sure that your charger is

a) working

and

b) is rated for NiMH batteries?

or

c) is switched to it's NiMH charging position.

One of the features of NiMH is that they continue to provide full current / voltage right up to the point of exhaustion. There's not the gradual trail off in output some that other battery types usually give. That's why manufacturers like them (a stable power source) but it can also confuse some chargers into believing that the batteries are fully charged when they are not.

[robertwgross]

In the NiMH battery department, like everywhere else, there are good ones and then there are bad ones.

Lately there have some very high capacity batteries coming on the market. It seems as though the capacity ratings are always exaggerated a little, and they are not uniformly exaggerated.

Some of the newest ones are a little picky about which charger they are recharged in. A generic charger will work, but a manufacturer-specific charger sometimes gets better results. Overcharging can be a killer.

---Bob Gross---

[CoolToolGuy]

Thanks for the replies.

The charger is the digital photo frame itself - you plug in the AC adapter and it powers the unit as well as charges the batteries. It seems to be working fine, since it powers the frame, and the batteries are getting a charge. But after sitting in my desk drawer for several months, the batteries must have discharged just from sitting. The batteries are Eveready AAs - maybe not the best, but not questionable online vendor quality.

I guess I will continue this charge/drain/charge process to try and reform them, but I don't know:
-What happens if I go into a 'drain' cycle and let it sit after draining for an extended length of time?
-What happens if I leave it charging for 2 or 3 days? Or longer?

Have Fun,

[robertwgross]

I guess I will continue this charge/drain/charge process to try and reform them, but I don't know:
-What happens if I go into a 'drain' cycle and let it sit after draining for an extended length of time?
-What happens if I leave it charging for 2 or 3 days? Or longer?


It depends.

There are complex chargers that do fancy functions to optimize battery life, and then there are simple chargers that do very little. Some chargers have a trickle mode. When the battery appears fairly full and charge current decreases, the trickle mode keeps a very low charge current going, sometimes in pulses. That keeps the battery "topped off" so to speak.

---Bob Gross---

[CyberDyneSystems]

Just based on what I've read here and my gut instinct.. I'd say the issue is with the Frames charger.

My guess.. if you were recharging only in a seperate dedicated charger of good quality (Lenmar or any of the good ones avaialble at Radio Shack) that the problem would go away. It sounds like the frame is literally killing your batteries.

[CoolToolGuy]

Just based on what I've read here and my gut instinct.. I'd say the issue is with the Frames charger.

My guess.. if you were recharging only in a seperate dedicated charger of good quality (Lenmar or any of the good ones avaialble at Radio Shack) that the problem would go away. It sounds like the frame is literally killing your batteries.

I don't think there is anything wrong with the frame. As I said, it sometimes sits unused for several months, and I'm not surprised that the batteries are discharging. It happens with all rechargeables if you let them sit.

This is one of those topics that gets under my skin a little. Several years ago, Black and Decker came out with a whole series of tools with these cute little rechargeable batteries (Versa-Pak), and I bit - bought almost every tool in the catalog, plus the 'good' charger. I charged up 8 batteries, leaving 4 in the charger. Didn't need them for several months, and when I went to get them, the 4 out of the charger had discharged, and 2 of the ones in the charger had shorted out (or something) from being in the charger for so long. Bottom line - I couldn't use the battery-powered tools when I needed them. So I contacted Black and Decker and asked a simple question 'What is the procedure to insure that my Versa-Pak batteries are fully charged at all times?' I went round and round with them for 2 weeks and the closest they could come was 'charge up the batteries a couple days before you need them'. DUH!? Sometimes I know when I'm going to need them, but not always. So the whole set of drills, power screwdrivers, tire inflator, dustbuster, etc, etc, was a waste of money. If they had a charger that kept the batteries fully charged without killing them, I would have gone for it. Now I'm back to AC power and extension cords for the regular household stuff. Strange enough, I don't have an issue with my DeWalt stuff, but that's the stuff I can usually plan for and charge up the batteries ahead of time.

Okay, I'll cool down now and get down off the soapbox. I guess I'll have to keep a close eye on this frame, and tend to the batteries.

Have Fun,

[Cadwell]

I've found a number of sources on the internet refering to this problem

You should never ever completely discharge your NiMH battery (nor a NiCd or lead acid battery for that matter). This can result in cell reversal. This happens when one cell has slightly less capacity than the others (a common occurrence due to small manufacturing variations). When the capacity of the weaker cell is exhausted, the other cells continue to pump current into it in the reverse direction, thus destroying the cell. This in turn destroys your battery unless you can take it apart to replace the offending cell.

Could it be that you left the batteries in the frame for a long time and they got competely discharged thus damaging themselves?

[CoolToolGuy]

I've found a number of sources on the internet refering to this problem

You should never ever completely discharge your NiMH battery (nor a NiCd or lead acid battery for that matter). This can result in cell reversal. This happens when one cell has slightly less capacity than the others (a common occurrence due to small manufacturing variations). When the capacity of the weaker cell is exhausted, the other cells continue to pump current into it in the reverse direction, thus destroying the cell. This in turn destroys your battery unless you can take it apart to replace the offending cell.

Could it be that you left the batteries in the frame for a long time and they got competely discharged thus damaging themselves?

Thanks for the info.

We'll see what happens - I have it charging now after running it till it died. This time I came back into my office and it was dead - but only for a minute or so. During the previous cycles, I was watching it and saw it start to 'go fuzzy' and turned it off.

I just turned it on after about 2 hours of charge, and it came on. So I guess I didn't kill it this time. I'll give it a couple more hours and see how long it lasts this time around.

I could just go buy a new set of AA NiMHs, but I am trying learn a little about them and how to keep this frame ready to go. I like this one because I can load a CF card and pass it around as if I was passing around a stack of prints - to show to the family or whoever.

Have Fun,