When to charge Eneloops?

[TyJo]

Bump. So an Eneloop at an open resting voltage of 1.2 volts or lower should be recharged... correct? Also, I just checked some Eneloops I rotate in my lights (they only go in 2 cell lights and are marked and matched, charged properly, rotated, new cells, etc.). They were charged and stored properly about a month ago, or slightly longer. I tested them and 2 different, cheap voltmeters gave me readings of 1.27 and 1.29v on the same cell, so 1.28 average (I accept the slight variation between the cheap volt meters). I am assuming this is a normal voltage for the eneloops... just making sure. Cells were charged using a Powerex (maha)MH-C9000 after a 1000 ma charge.

 

[Mr Happy]

Hmmm, even the cheapest voltmeter should read accurately to the 10 mV level. One or other of your voltmeters is broken. Does the battery need replacing?

Assuming the voltage readings are correct (doubtful), your Eneloops are under charged. They should be reading in the 1.33 to 1.38 V range. Did you leave them to do the 2 hour top off in the C9000 after "Done" appeared?

 

[Lynx_Arc]

Personally I think voltage (not under load) is a good indicator of charge level once you get attuned to your nimh batteries. If what you are using the batteries in you (under average use) only get 1-2 hours of runtime you will want to charge batteries at higher voltage than if your runtime is 10-15 hours because capacity left is related to runtime and if you only have 25% left on a 2 hour runtime that means only 30 minutes while 25% of a 10 hour runtime equals 2.5 hours which unless you plan on being away from a charger or a battery swap is typically useful. I typically charge batteries below 1.28v (no load test) as there is less than 50% left and charging and/or swapping batteries is just as easy as pulling dead batteries out of something and charging them at that time. Nimh are meant to be used and charged often so even a top off charge is worth the effort over endlessly testing batteries and just putting them back in. If you get 500 cycles out of batteries that would be one charge a week for 10 years.

 

[TyJo]

Hmmm, even the cheapest voltmeter should read accurately to the 10 mV level. One or other of your voltmeters is broken. Does the battery need replacing?

Assuming the voltage readings are correct (doubtful), your Eneloops are under charged. They should be reading in the 1.33 to 1.38 V range. Did you leave them to do the 2 hour top off in the C9000 after "Done" appeared?

I rechecked my batteries. There is a small possibility that I had measured partially used batteries since I just changed my rotation system. The readings are within 1/100 decimal, or only vary by 1/100. I doubt that I left the batteries in after it said done. I checked some other batteries and 2 different sets read 1.40 and 1.43. I will leave the batteries in for 2 hours after charging from now on.