Hi!
I have two new li-ion 26650 4800mah unprotected batteries bought 2 days ago. I use a charger for li-ion and li-fe batteries with a balanced cable.
When I charge these two new batteries it charges them fast up to 4.19-4.2V each. But then when I disconnect the charger the batteries starts to lose their charge up to 3.4v themselves. I have another two batteries with the same characteristics from the same supplier and they work ok. Two old batteries charges like 10 times longer and work great. What can it be?
Assuming both sets of batteries are being given the exact same charge pattern with the exact same charger it seems to me that you need to put the question to the supplier.
...R
What can it be?
Cheap manufacturer's rejects bought on eBay?
Are you measuring voltage as soon as you disconnect the charger? Or perhaps you're measuring while they are still being charged?
When you have charged them disconnect them from the charger, leave them to rest for 5 minutes and then measure the voltage. If it's less than 4.1V the batteries are bad.
If they're o.k. after 5 minutes then leave them overnight and measure again. If the voltage has gone down below 4.0V then the batteries are bad.
Good li-ion batteries will keep a charge for months.
Steve
Of course I measure them disconnected. I’ve tried to load them. Charged up 4.2 each with an 11 ohm load they lose their charge down to 3.6-3.4v in 5-8 minutes and then discharge slowly as if it is their real capacity.
Charged up 4.2 each with an 11 ohm load they lose their charge down to 3.6-3.4v in 5-8 minutes
That is normal behavior.
Measure the actual capacity in Ampere hours, until the voltage drops to below, say 3.0V, and compare the result to the manufacturer's specs.
Example curves for a 26650 3 Ah battery:
Actually it could be normal if it were a LiFe battery. But I have Li-ion ones and their nominal voltage is 3.7.
LiFePO4 batteries are 3.3V nominal and its pretty clear that's exactly what the new ones are! Whether
they are 4.8Ah is another question.