Over-Discharging NiMHs w/ Energizer Hard Case Pro 2xAA LED

Hey guys,

I have a question about over-discharging my Maha Powerex 2700MAH cells when using this light. I've been doing a lot of reading, searches and thinking about cell conditioning, battery chemistry/capacities and charging methods. I know Silverfox is the go-to guy for this kind of stuff, so perhaps he or someone else has some advice.

I use this floody little light to read at night in bed. Recently, I've fallen asleep TWICE with the flashlight on and woke up to find it completely dead. Clicking it off and then on again in the morning produced just a blip of light and then nothing. I made sure to throw the cells into my Maha MHC204 in the morning on both occassions. Even before I discovered this wonderful site and its wealth of information, I knew that draining the cells like this can damage them/shorten their life. Why did I do it!? - Twice!

Do you think this event has turned my cells into crap? These cells are about 1.5 yrs old and have not gotten much use. I never cycled them, and basically just used them to power this flashlight. 2 cells sat charged while 2 were in use. I never performed maintenance charging.

A few months after these narcoleptic episodes, I bought a Nitecore D10 and finally delved into the CPF world. This purchase pushed me to get a more sophisticated charger. I picked up a C9000 last week and found my cells were in a pretty bad state. After 3 Charge/Discharge cycles at 1000mah/500mah the cells came back to life but were only showing about 2200mah capacity. I discharged them at 500mah and put them back in for a break-in cycle. They have almost finished this cycle. Once they finish, will a midpoint voltage reading during discharge give me an answer as to whether or not they need to be retired? Does cycling reduce a poorly performing cell's internal resistance?

Thanks.

Hello Dannstrait,

Welcome to CPF.

You will have to measure the discharge capacity to see if your cells are crap. When they drop below 80% of their initial capacity they are crap, and usually they have lower mid point voltage as well.

Sometimes you can revive a cell through charge/discharge cycles, but the best way is to use the Break-In function on the C9000. I believe the 2700 mAh cells come in at around 2500 mAh, so you are still above 80% with your 2200 mAh.

Tom

dannstrait said:

...I have a question about over-discharging my Maha Powerex 2700MAH cells when using this light...

...Recently, I've fallen asleep TWICE with the flashlight on and woke up to find it completely dead... ...I knew that draining the cells like this can damage them/shorten their life. Why did I do it!? - Twice!

Click to expand...

Take a look into NiCDs for your evening escapades! They can handle this type of abuse better than NiMHs.

CLICK on my Sig Line LINK and read the Theory articles at Battery University and Battery FAQ for more info.

Wow, thanks TTA. That's a plethora of info! I wish I had found it before I posted.

Thanks Silverfox...the break-in cycle completed last night. 2 cells showed about 2400mah capacity and 2 showed around 2300mah. I guess they're not recycle bin material just yet.

When I first took my C9000 out of the box I threw these cells in at a 1amp discharge. Within 5 minutes all four recently-charged cells had fallen to .9V and the cycle was "done."

So last night, after all this cycling and resuscitation, I placed the fully charged cells on a 1amp discharge once again to observe their revitalized performance. They held their voltage well enough to complete the discharge cycle with an average of about 2250mah capacity - definite improvement.

Currently, I have them going on another break-in cycle. After completion, I plan on placing them on the shelf for 7 days then running a 500mah discharge cycle to observe self-discharge performance. I'll post back with results.

So a week ago, after a standard charge, I placed these cells on the shelf to test for self discharge; they showed capacities ranging from 2300mah to 2400mah. Yesterday, I threw them on the C9000 for a discharge @ 500mah. The voltages looked pretty low except for one cell that held around 1.17. The other cells started below 1.10 but crept up to around 1.10-1.12 for most of the discharge. They finished discharging with capacities between 2037mah and 2100mah. In conclusion, 3 of the 4 cells seem to have pretty high internal resistance but are still above the 80% capacity and 80% self discharge thresholds.

I have 4 other identical cells that I did not over-discharge. They have shown much better capacity and performance. I have not run a self-discharge test on them, but their capacities are between 2400mah and 2500mah and their midpoint voltages on discharge average 1.17.

Now that I know better, I'll try to keep my cells in their happy place. I've discharged the 4 abused cells and put them back on the shelf. I figure if I need to use them, I'll plan ahead so that their performance will be as vibrant as possible. I'll give them a cycle every month or so as recommended.