Do you discharge your NiMH batteries?

[carguy]

My Watson 8-bay Rapid Charger arrived. I'm charging my eneloops now (AmazonBasics Black AA should arrive soon).
This charger has a 'discharge' feature. Is this recommended each time you charge or to do periodically?

Thanks!

 

[WayneF]

Periodically at absolute most. Charge and discharge is not really good for batteries. My Maha charger suggests their Refresh mode (which includes charge, discharge and recharge) every 30 cycles. My notion is that is just in defense of their option, it is not needed for NiMH. Primarily it is only for testing charge capacity, which it shows. I never do it, and my Eneloops last forever.

Do charge the new Eneloops before first use. They are only maybe 70% charged at the factory.

 

[carguy]

Yep, those in the charger I've had since last fall. Discharging them now as it hasn't bee done before.
The new set will be charged to 100% once they arrive.

 

[Pretzel]

At times, once a battery starts displaying shorter life spans, a couple of discharge/recharge cycles will extend the life, but with the NiMH batteries, it's nowhere near as crucial as it is for NiCad packs. That's the advantage of the NiMH - longer shelf life and HUGE improvements in what they called "charge memory".

I'd say about once a quarter at most, though, it's good to let a battery drain down until device shut-off and recharge back to full. I try to do that with my rechargeables twice a year, personally. If you do it too often, you're actively decreasing the number of recharge cycles available.

 

[Bob Blaylock]

Nickel-Cadmium and Nickel-Metal-Hydride batteries do need to be fully discharged from time to time; otherwise, they lose capacity.

All other kinds of rechargeable batteries do not, and it is best to avoid fully discharging them.

 

[WayneF]

And my philosophy is to recharge NiMH and Lithium Ion early and often, when possible. As opposed to letting them run down too low.

 

[Pretzel]

And my philosophy is to recharge NiMH and Lithium Ion early and often, when possible. As opposed to letting them run down too low.

With Lithium Ion, I've never seen anything to contradict that thought. With NiMH, it still works as they're very low maintenance. It does shorten the usable overall life-span of the NiMH, though, and eventually reduces the "per charge" life as well, but it's drastically less of an impact than in the old Ni-Cad days. (I still remember the old purple "Shack" rechargeables. Does that make me old?)

 

[WayneF]

Batteries are like lead-acid car batteries, always keep them charged, continually with trickle chargers when necessary. It's tough on their life to run low or to sit low. True of deep cycle batteries too, but they are made different to stand up a bit better to it. They are also better off when recharged early and often. Light cycles are better then deep cycles.

Sitting low is not hard on NiMH (said better stored around 40%), but charge and discharge is hard on them. Specs give us a life expectancy of number of times. Which is many, but I see no point of intentionally adding to that usage, esp not with deep cycles.

The only exception is NiCd, said to have a memory for repeated same conditions (said of satellites circling the earth, which is extreme, precise and frequent repetition, but other uses seemingly are exaggerated). Most of the devices (toothbrushes, drills, etc) with NiCd provide a continuous charging stand for them, which is still recharge early and often.

In the past when I was dumber, I tried twice to intentionally fully discharge NiCd (like in a dustbuster), as seemingly instructed, but it ruined (killed) the batteries both times.
My notion now is that it's better NOT to do stupid stuff.

I have a 2008 Prius, which its electric motor is powered by well more than a hundred NiMH cells (I forget exact number, but in series, its about 200 volts). These are simply just D cells, except made square, and multiples packed in steel cases. All in series, and about 7 AH capacity at 200 V, NiMH.

Point is Toyota provides computers to NOT let them be charged over about 80% and NOT under about 40% (ballpark, I forget exact numbers). The batteries are simply cut off when low, and you're on your on with just the gas engine. Electric is only used for acceleration, but driving up Pikes Peak was interesting, losing half of capability about half way up.

But with these 80% to 40% limits, they warranty the batteries for 8 years. And there are few stories about the batteries. Mine is 7 years now. I have replaced the 12V battery once.