Bad experience with an Ebay battery dealer

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lightning
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Bad experience with an Ebay battery dealer

Post by lightning »

Bought 3 dozen "2500Mah" AA NiMH batteries from a dealer on Ebay (gadgetslink). Was planning on making some long-lasting Tx packs. He's sold a LOT of stuff.
Here is the link http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... 0191377479
Well, they are shipped from Hong Kong, so that doubled the price of the batteries, but they were still only just over a buck each.
Well, I guess you get what you pay for!
Soldered some up into Tx packs, some I did not. Decided I should probably cycle 'em to see what they were really capable of.
Well, they cycled at 650MaH +/- 25 Mah! Not much more than a quarter of their rating. [:(!][:(!] Soldered packs vs. unsoldered in a battery clip made no difference.
That was after at least five cycles with 3 different cyclers set to a cut-off voltage of .9V/cell
Contacted the seller who will take them back for a refund, even refund my return postage, but not the original $18 postage to ship 'em out.
So I'm out that $18 plus a bunch of work and have no batteries.
So be warned - if it looks too good to be true, it probably is!
Makes me wonder if anyone else has even bothered to test them.
Vapor52
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Post by Vapor52 »

I bought some from Allbatteries.com They also did not come up to there ratings, but they were'nt that bad--1100's came up to about 950. They do seem to be holding up OK----------rick
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lightning
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Post by lightning »

Hi Rick, with the loads we put on these things I figure anything over 80% is OK. If this batch had hit 2000MaH I would have used them, but 650MaH - NO WAY!
Don Pruitt
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Post by Don Pruitt »

Keith,

Your 80% figure is probably a good rule of thumb and I will share with you the reasons why.

For 10 years I worked in R&D for a major cell phone manufacturer and during that time I spent much of it writing specs for and testing NiMH batteries. We had an on going battle with various battery vendors. We would spec a battery for 750 mAh and when we tested a sample it would typically fail somewhere between 600-700 mAh. The vendor would accuse us of improper testing and we would respond that we tested the product in the environment in which it was to be used. Big difference and here is why.

Some manufacturers rate their products conservatively. As an example, they will engineer a 750 mAh battery to deliver 825 to 850 mAh so they can realize a 100% yield at 750 mAh. The batteries are typically priced accordingly.

Other manufacturers will rate their products optimally. Which means that the advertised capacity is the maximum capacity that battery will deliver when tested with the optimum parameters.

Another variable is that some retailers will purchase batteries that failed the manufacturers specs. Sometimes the manufacturer will simply re-label the battery at a lower capacity but this is time consuming and increases the cost. Most will just sell them at a reduced cost. In this case if you buy one of these batteries you will be purchasing a mislabeled product. (Some people are simply dishonest and they will lie to you)

The IEC defines the standard test parameters for NiMH as a charge rate of 0.1c and a discharge rate of 0.2c. This is the most efficient rate that will produce the highest capacity. The charge duration should be; (Rated Charge Capacity (Ah) / Charge Current (A) * 1.4).

For a 2500 mAh battery you would charge at 250 ma for 14 hours.
2500 / 250 * 1.4 = 14 The extended charge time is required because the battery is not 100% efficient. Battery efficiency is usually around 80%.

The discharge rate of 0.2c keeps the battery operating in its most efficient temperature range and inline with the battery chemistry. The battery discharge should be terminated when the voltage under the rated load reaches 1 volt per cell. Example: a four cell, 4.8V battery is considered discharged when the voltage under the 0.2c load is 4.0V.

So, the bottom line is that the way we usually use our batteries we seldom will see them perform at the advertised capacity.
Vapor52
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Post by Vapor52 »

Great tutorial Don, helps us to understand greatly--------rick
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lightning
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Post by lightning »

Good stuff Don.
I was charging at .2C (500Ma) and discharging at .3C (750Ma) which is why I would have been OK with a 2000 MaH reading.
But I was discharging to 3.6V (.09V/cell) using an Accu-cycle Elite cycle.
My numbers (650MaH or so) were the average of five cycles.
Seller tried to wriggle by saying I'd soldered 'em.
Well, I had soldered SOME, but not all, so I tested the ones I had not touched - same result.
That shut him up!
Don Pruitt
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Post by Don Pruitt »

Keith,
I agree, the results you got were way out of line. I just bought and returned a 2500 mAh TX battery off of Ebay at what I thought was a good price of $9 plus shipping. It was advertised as being for a Hitec TX. When it came in I tested pretty much the same as you did and got consistent readings of 1900 mAh. I would have kept the battery except that the leads were for a 3 pin connector and my Eclipse 7 has a 2 pin connector. The pin size was also different so I couldn’t just push the pins out and swap the shell. After an email and attached pictures he agreed to take them back. I shipped them back on Saturday and now I will see if he credits my PayPal account.
Vapor52
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Post by Vapor52 »

Don, was this the Allbatteries.com site?-------rick
Vapor52
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Post by Vapor52 »

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lightning
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Post by lightning »

Hey Rick, that might be the way to go. What would you charge it with? I don't have a LiPo charger (or balancer) but my Field Charger MkII is supposed to charge Lipos to 80%.
Vapor52
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Post by Vapor52 »

If you don't have a lipo charger I wouldn't buy one. I know that with my 1650 Ni MH I could fly two days of combat with no worry, I assume with 2500 Lipo that has little surface drainage you will sport fly 2 weeks or so before charging.
Don Pruitt
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Post by Don Pruitt »

Rick,
No it wasn’t Allbatteries.com it was:

eee4u
Elegant, Exquisite Electronics For You
581 Grove St.
Newton Lower Falls, MA 02462

He is still offering them for sale at
http://cgi.ebay.com/1-RC-9-6V-2500mAh-S ... dZViewItem
Vapor52
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Post by Vapor52 »

Don, I was wondering because I was thinking of trying Allbatteries -------rick
Alex Treneff
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Post by Alex Treneff »

Keith,

The easiest way to get (presumably) reliable batteries is to go to Sams Club (or Wal-mart) and get camera AA's.

I bought some Sanyo 2300 mAh (rated) Ni-MH from Mr. Ni-Cad (http://www.batteriesamerica.com/) at the 2003 Toledo show for digital camera use. I cycled them initally to see how strong they really were - 2900 mAh!

I cycled them again a couple of weeks ago because they seemed to be going bad. Now, four and a half years later they are down to ~1650 mAh, still usable. But I'll have to replace them sometime.

I figure any of the name brands at Wal-Mart come out of the same factory in china, so they'll all work. I've got them in my transmitter and in various planes.

And the camera AAA's work great for combat planes. Wal-Mart has a 4-pack of off-brand AAA's that claim 1,000 mAh for $5.96. I haven't cycled any of them, but they're in all my combat planes and work great.
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lightning
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Post by lightning »

Thanks Alex, had not checked WallyWorld. I have a competing store to them a lot closer and they want $21 for 8 AA (2000Mah) or AAA (800Mah) Energizer rechargeables.
Decided that was a little over the top!
I'll take a look next time I'm over that way.
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