MidnightDistortions
Flashlight Enthusiast
The only thing i can think of is you had them in a device and they kept discharging past 0.9 volts. In my experience any device that runs the batteries totally flat go bad. They don't always reverse charge but the ones that do won't work anymore. The ones that go flat can eat up a lot of cycles. My suggestion is if you do not have a multimeter to get one and do some testing on those other cells in the device you had them in to check the voltage. Best to back track and redo the tests the best way you remember how you had the cells. If you left them in a device unused, the device may still be draining the cells (normally at a slow enough rate not to be a huge concern) such as a flashlight that will continually drain the cells at a slow rate.
If your charger is overcharging the cells, i'd get rid of that charger for one that will not overcharge the cells. Eneloop Pro's doesn't specify how long they hold a charge for 3 years or 5 years. I'm curious if there's any testing done on this. I actually consider anything under 1.1 volts deeply discharged. Usually i'll try to recharge the cells at 1.22-1.26 volts and then refresh them every 6-12 months but sometimes i forget to check the voltage and the cells are around 1 volt and need recharging. It seems especially for the pros it's not a good idea to run them all the way down. I also hear of PowerEx 2700mAh cells only lasting a couple of years, but there are people who say they have been using the cells for 6 years and they still work so i'm guessing that the ones who are still using those cells for 6 years must not use them much or recharge them before they get below 1.1 volts.
Also i am curious as to maybe these cells should not be fully charged (when put into storage) that they should only be partially charged (or partially discharged) to avoid the high IR. I know on traditional HSD NiMH cells leaving those in a charged state without use will increase the IR on them. I've run into some cheap cells that have been fully charged a few times and not put in use that have developed high IR, it might be a good idea to leave them with a 40% charge (or maybe less) when put into storage. I think testing this would help some people out that have Eneloop Pro cells. Regular Eneloops i don't think it will make much of a difference but should not be topped off if they are not being used much. This also makes it more apparent that i wanted to use some AAA to AA adapters on low drain devices where AAA cells would be more beneficial in clocks or other low drain devices as they don't hold as much capacity and the cells are a bit cheaper.
As for using high capacity cells, the experiences i had with them degrading, they'll degrade faster if they were completely discharged past 0.9 volts. The only suggestion i can consider if you absolutely need those cells running is to get a charger other than the c9000 which doesn't completely charge the cells unless you let them sit on there for 2 hours or more past the 'done' stage. On top of that on completely depleted cells a slower charge rate imo is better as you will get a more complete charge because Eneloops are usually charged up to 1.55 volts and i don't think the 2 hour top off is enough for the Pros to be considered fully charged. 1000mA on the C9000 for Eneloop Pros might not be a good idea, i would probably choose 500mA, less if cells were discharged under 0.9 volts. I don't have a set of Eneloop Pros (AA) to effectively test this theory out, i could try the Duraloops out to see how much capacity is lost to a possible premature cutoff. The C9000 appears to charge Eneloops and i'll choose the 1A when the cells are around 1.26 volts but as the voltage is lower, i tend to lower the charge rate as well.
