Testing a NiMH battery charger

"Dope"

The batteries get hot and you can feel that with your fingers.

Means they are charged.

..... Phil

Are YOU "for real"????? Define HOT, smartass.

Idiot.

yep, be more specific. "not very long"

NiMH batteries don't hold a charge for long. Especially high capacity ones. Especially cheap no-name ones. I'd not expect more than a couple of weeks of useful storage. Enloops or equivalent hold a charge much longer.

Temperature charge termination is a BAD way to charge cells. It can work well if you fully discharge before recharging. Problem is that if you put in a nearly charged cell, you can do damage before the cell has a chance to heat up enough to trigger the termination.

If you mean they don't put out as much energy as expected, that's a different issue. Depending on the load current and the device shut-off characteristic, internal battery resistance can cause the device to shut down long before it's used up. Cameras are especially bad in that respect. I've got cameras that run well on one battery vendor, but not at all on any other.

It's like anything else. If you want long service life, buy premium cells and chargers.

Mike - Thanks for the reply. I agree temperature change sensing isn't as good as sensing voltage changes. The batteries are Harbor Freight, so they are cheap, but I've been using these types from them in AA & AAA for years with no issues in things like remote keyboards, lower drain items. Bought a new set for a CAMERA, as you said. The camera does have a setting for cell type, and a discharge function, which I've used to deplete them completely twice with recharging. I know this is especially an issue with cameras. Interesting about the internal resistance.

You may be right about springing for better cells, at least in this high drain usage. Only trouble is my $$$ is a bit limited at the moment ;-/

Dan

Not so. I've put AA NiMH cells in a flash, that were charged months earlier, and they powered it well. This is an urban legend that has little basis in fact.

If it's the only method of termination, yes. But it's necessary to prevent overcharging, especially when the manufacturer recommends "slamming" the cell.

Good cells aren't expensive. A 16-pack of 2700 mAh MAHAs at Thomas Distributing is less than $3 per cell, and they throw in plastic cases and a carrying case.

My experience has been that a 2700 mAh cell has about the same capacity as

I have two of these chargers, and paid about $40 for each -- when they were on sale. You might want to wait.

If you do the research, you'll probably decide that anything bought from HF is CRAP. That goes double for anything with a battery in it.

They succeed because many people, like me, buy a tool for a job and rarely, if ever use it again. I have a boatload of HF stuff in that category, but I'd not buy it for a long-term use where reliability was an issue.

Saving a few bucks on something that doesn't do the job is not being frugal.

Use the HF cells in low-drain devices. Buy good cells for the camera and a new smart charger. The HF charger probably won't be friendly to your expensive cells. Enloops are highly regarded cells, but I guess it also matters what color the top plastic is. Japanese vs Chinese manufacture.

Ebay cells are a crap shoot. I'm sure some of them are genuine, but I wouldn't bet money on it. My limited experience with EBAY cellphone batteries suggests that their specs are exaggerated.

I've had several cameras that ran on AA cells. NONE of them were worth a crap. I don't know how they ever sold them new. Must be some degradation in the sensing circuitry that makes them all useless on NiMH now.

Sometimes, you can find lower capacity cells with lower internal resistance, but I don't know how to tell without actually measuring it.

Charging Nickel-metal-hydride

When the cells get really hot, they are what I consider to be overcharged. By the time the thermistor gets really hot, it's too late. The cells start to get warm when the battery is at about 80% charge. The charger is suppose to switch to trickle charge at that point. Some do, but a few try to guess when they'll hit 100% and continue with the fast charge. That usually works with new cells, but is a great way of destroying older cells.

One of the really dumb ideas in chargers is to put a fan on the battery charger. This will keep the battery cool so that the thermistor does not properly detect that the battery is nearly at full charge.

The only way to properly determine the capacity of a battery is with a discharge tester. I use a West Mtn Radio CBA II It generates curves like these for NiMH cells: Incidentally, that was my attempt to verify that it takes a few charge cycles before a NiMH battery reaches full capacity. Apparently, it's true, although the difference in capacity is rather small.

Favorite NiMH battery is Sanyo Eneloop: It loses about 10% capacity almost immediately from self discharge, but then stays at that level for many months. Available at Costco at

Agreed. I needed a reciprocating pneumatic saw and bought two from Harbor Freight. That's when I discovered that the blade travel was about 1/8". Useless junk.

There are now 3 or 4 varieties of Eneloop batteries. Five if you include Chinese fakes. There was a web page showing how to identify the various varieties, but I can't seem to find it.

I buy quite a few eBay cell phone batteries. My guess(tm) is that I've bought and used about 200 batteries from random vendors. Many of them get tested with my West Mtn Radio CBA II for capacity. I have had some obvious lemons, but they were simply dead, as in no output. Tested capacity is varies somewhat from LiIon cell to cell. The switchover from explosive LiPo batteries to safer varieties seems to have resulted (i.e. not sure) in about a 10% decrease in capacity. However, the battery label remains the same as with the LiPo including the rated capacity.

Neither do I. So, I measure it. Some typical results: etc. My results for specific battery follow these tests almost exactly.

On 10/28/2012 9:22 AM, Jeff Liebermann wrote:

Thanks everyone for the great info on the batteries! I'll have to go back through all the links, but I appreciate the input!

On Harbor Freight, my experience with them is that if you buy carefully, you can get what you need at a very good price. I've always had very broad interests (my downfall, some have suggested... ;-) and I personally own well over 20 grand worth of tools of all kinds which I have amassed over the years, from a tiny Swiss watchmaker's lathe to a full size PowerMatic cabinet saw and 8" jointer (woodworking is my real passion). I also have a complete set of professional grade automotive tools (mostly 30+ year old Craftsman & Snap-on). I do know good tools. I would not buy something requiring a high degree of precision, such as a jointer, from HF, but I have quite a few pneumatic nailers, impact tools, and even a compressor of theirs which have all served me quite well for years. I also have a very nice 3/4 HP drill press of theirs, as well as one of their tool chest side cabinets. All very servicable. Is everything they sell the best of its kind? No, of course not. But for the price (particularly if you combine a sale with one of their ubiquitous 20% off coupons) I have had no complaints overall, especially for tools I only use on occasion. And they're very easy with returns, if you do have a problem. I also have an HF clamp on multimeter which just yesterday I was using to measure the current drawn by a heater. Out of curiosity, I checked its readings against an inline measurement using a Fluke I also own. Dead on.

Dan