How Long Should NiMH batteries hold a charge?

[david_gardner2]

My company bought a digital last year, and 8 Energizer Nickel Metal Hydride

batteries to keep it going all day. I personally charged all of them to full

about two weeks ago. Today I went to do some shots for a client and they were

all dead. I know they'll lose charge over time, but not two weeks, right? Bad

batch of batteries? Am I missing something obvious?

[crabseye]

Nimhs should be good for at least 5 years/500 charges.

[david_gardner2]

Thanks for the answer, but I think your answer if about the lifetime usefullness of the batteries. What I'm really asking is, "If I charge them and put them on a shelf, how long should they hold a charge before I need to charge them again?"

[todd peach seattle, washi]

The self-discharge rate for NiMH is on the order of 1% a day. So 30% for a month.

 

Sounds like something is wrong with yours somewhere along the way.

[godfrey]

I do not rely upon NiMH batteries to hold a charge, unused, for more than two weeks at the

outside. They might do that when not loaded into a device and stored in a proper insulated

battery storage box, but it's unwise to count on it.

 

I charge mine on a schedule every week so that they are ready in the event of unforeseen

need, and charge them all the night before scheduled jobs. And spares, just in case.

 

Godfrey

[leicaglow]

I agree with Godfrey's 2 week rule. The other thing is that I always label the batts with a date code and a number that indicates which group they belong to. I don't try to stretch life out of failing batteries by mixing batches.

[d_gillespie]

Michael has a great point about mixing batches, label or color code to keep the sets together. Experience has slapped me twice in this arena. I think two weeks is the edge, also why not charge them on the way out the door the night before your are scheduled to shoot. Too late now, but maybe next time.

[david_gardner2]

Thanks for all the info. The camera is kept locked up, so getting to it alone is a minor nuisance, let alone getting it the night before and charging batteries. What I may start doing, however, is keeping the batteries at my desk and charging them regularly.

[thomas_sullivan]

I use NiMHs for everything these days. Well, in my case everything is camera and flashlites.............electronic flashes I never keep the batteries in them as I don't use them that much. but anyhow, comparing the camera (in this case a Canon A80) and your typical small emeregency type flashlite, I find the flashlite far outlasts the cam.....both sitting there doing nothing.........and yeah, 3 weeks is about max I get out of the cam, sitting there doing nothing. The flashlite keeps chugging along looooooooooooooong after that.

 

I think that even though you turn the camera off, there is still circuitry that is energized........so the camera does drain the batteries thru that. The flashlite is completely off, and lasts much longer (actually it has never drained just sitting there.......only when I use it for a long time with it on)

 

Probably just taking the batteries out of the camera would be sufficient for your purposes.

[crabseye]

Sorry David, I answered everything except what you were wondering.

 

2 weeks doesn't seem right.

 

I use Nimh's in a universal remote control, nightly use, 4 AAAs, and they last just about exactly 2 months. I would imagine that usage exceeds trickle discharge. I think you might look into some new batts. These are the discontinued Rayovac IC3's that recharge in 15 minutes. Duracell and Energizer make similar rapid charging batts too.

[robert lee]

The self-discharge for NiMH is about 10% on the first day, then about 1% per day thereafter.

 

I've a couple of digicams that use AA and AAA cells. Practically, I can get a couple of hundred shots on a set fresh off the charger. After two weeks, maybe 10 shots before the camera flashes low power.

 

The kind of longer term storage scenario you get depends on the device you're trying to power. Digicams are bad in that they all require very high instaneous power. On the otherhand, I've NiMH hold enough charge to power fully LED lamps after a 1 month standby.

 

For standby type digicam applications, you need to go with disposable lithiums. I've a little Sony digicam in the glovebox. It's still showing full charge (and usable) after 1.5 years with a pair of Energizer AAA lithiums.

[conrad_hoffman]

Suggest a good read at www.batteryuniversity.com

 

My guess is, along with the usual and normal initial and longer term energy loss, you may not be getting them fully charged to begin with. With "fast" chargers, you only get a percentage of full charge. It takes a longer time at a much lower rate to top them off, after which they should be disconnected from the charger and not allowed to trickle charge forever, which is also bad for them.

[tom_jenner1]

I always top off my NIMH's right before I use them. I go through a lot of batteries in my work so I also take the time to match them and throw away the lowest performing ones (I buy in bulk).

 

-Tom

[craig_gillette]

You need to get them charged up before use. I had 3 sets of different makes and slightly different capacity when using a Fuji s602. I never even tried to go 3 or 4 days with a charged set sitting there and expecting reliable use.

 

Digicams are very voltage sensitive. Assuming they lose 10% the first day and 1% each day after that, at 2 weeks you are down 25%.

 

Putting a "set" together and keeping them together in use and in charging is a good idea. It was easy with mine with 3 sets/3 brands.

[joseph_wisniewski]

There are no hard and fast rules for NiMH discharge. You can't say 1% per day, or 10% in the first day, 1% thereafter. The self discharge rate varies with temperature, the particular chemistry used in the battery, the thickness and nature of the separator material. In general, really high capacity batteries (like 2700mA-H Sanyos) or really low resistance batteries (like 1 hour or 15 minute charge Energizer or Duracell) have the worst self discharge rates, and being essentially dead in just two weeks (that's 7% per day) isn't unusual. At the opposite end of the spectrum, there are new "precharged" NiMH cells that only self discharge about 5% per month, so they're at 1/2 power even sitting for a year. (Oddly enough, they're made by Sanyo, too, so the fastest and slowest self discharging cells come from the same company).

 

Things get worse if you use a charger that charges two cells in series. This allows batteries to become unbalanced, the weakest cell just keeps getting weaker until it's got 1/2 or 1/3 the capacity of the strongest cell in the set. So even batteries that are only discharging 2% per day still look like they're dead in two weeks, because the weakest cell was only at 30% to begin with, and 2% per day sucks it down to nothing in 15 days. If the charger has one LED per battery, it's the good kind, each cell is charged independently. If there's half as many LEDs as batteries, you've got the charger than unbalances cells.

 

So, the correct answer is: the right cells with the right charger can sit for a year, the wrong cells and/or the wrong charger can drop that down to your two weeks, and you can see anything in between, 4 weeks, 3 months, etc. with little rhyme or reason.