I have found that all of the AA and AAA NiMH batteries that I have purchased on eBay since September 2007 are bad and are not 2600 mah as advertised. So far I have purchased about 100 of these batteries, all from dealers in Hong Kong. Most are branded "BTY 2600mah" and some are light or dark green with no-brand-name and are simply marked "AA Ni-MH 2600mAH 1.2v".
m_spasov has also posted a good guide with additional info about his experiences. (Beware! Fake "BTY" Ni-MH rechargeable AAA/AA Batteries!)http://reviews.ebay.com/Beware-Fake-quot-BTY-quot-Ni-MH-rechargeable-AAA-AA
Here are a few ideas about how to test them if you do buy them.
The easiest way to test AA and AAA rechargeable batteries is with one of the commercial chargers/analyzers such as the Maha MH C9000 or the La Crosse BC-900. These were previously fairly expensive but the price has come down. The Maha C9000 is about $70 and is top rated. I prefer the La Crosse BC-900 because it is much smaller, cheaper, and comes with 4 AA and 4 AAA Nimh batteries. The BC-900 is available on ebay and Amazon.com for $39.95.
If you don't want to spend the extra money on an analyzer, you can accomplish the same test results using some fairly simple methods and tools.
Make sure you charge the batteries when received and before testing. My first test is to put two cells in an ordinary two cell flashlight and leave it on for about 1 hour. This puts an approximate load of about 600ma on the batteries. If the flashlight is dim or out after 1 hour, one or both of the batteries have low capacity. With most of the batteries that are bad the flashlight goes out completely after about 50 minutes.
A better test is to apply a resistive load and monitor the voltage with a multimeter (voltmeter). You will need a multimeter, a battery holder, and a 5 or 8 ohm resistor. The 5 ohm resistor is approximately 240 ma load at 1.2 volts while the 8 ohm resistor is about 150 ma load.
Put the charged cell in a battery holder and attach the voltmeter. Clip on a 5 or 8 ohm resistor and record the time and voltage. Monitor the voltage until it reaches 1.0 volts or less and record the time and voltage. Remove the load. With bad batteries it will take 1 to 2 hours to go below 1 volt.
If the voltage falls too rapidly or the cell reverses voltage, it is bad.
The mah capacity can be calculated from the data as follows: (Milliamps load (150ma for 8 ohms)) multiplied by (Time in minutes to reach 1.0 volts) divided by (60 minutes per hour) = Approximate Mah capacity. For example if it took 90 minutes to get to 1.0 volts with an 8 ohm resistive load: 150ma * 90min = 13,500ma mins / 60min/hr = 225mah capacity.
Most of the AA batteries that are bad are only 200 to 400 mah capacity.
If you have a lot of batteries to test, it is really worth your while to get one of the commercial chargers/analyzers mentioned above.
One more thing about buying batteries on ebay. You can ask the seller a question about the product. Click on the "Ask the seller a question" link on the product auction page and ask something like "Can you guarantee that these 2600mah Nimh batteries will work in my digital camera and that they have a capacity of 2600mah?" (Change the 2600 to 2500, 1000, etc. depending on the stated capacity). If the seller does not answer or evades the question, do not buy them. Several sellers have fully refunded the price paid for defective batteries, including shipping, without having to send back the bad ones.
hollidayp1 080928 0210