eneloop - best to charge up before they go flat?

[CoolHands]

is it best to charge up eneloop regularly before they go flat, rather than run them flat & then charge them? Or doesn't it matter? (AA and AAA if it mattesrs)

 

[Marduke]

Shallow discharges are better, assuming you are not using a simple ("dumb") timer based charger.

 

[TakeTheActive]

is it best to charge up eneloop regularly before they go flat, rather than run them flat & then charge them?

What's your goal?

1. Maximum number of CYCLES
   .
2. Maximum CAPACITY per cycle

Choose ONE!

 

[Mr Happy]

Unless you are running a single cell device, you should never, never, never run NiMH rechargeable batteries flat. Always recharge them before they show a noticeable drop in output.

The reason is that if two or more are in series, then the first one to run down is likely to get reverse charged by the others that still have some power left. Doing this repeatedly will seriously damage a battery.

 

[zipplet]

Ditto with what Mr Happy says. There have been many discussions about that on this board and reports of gas buildup due to one cell being overdischarged (and forced into reverse charging).

 

[bltkmt]

My issue is that I use them in devices like remotes or computer mice, where I don't know they need charging until they are dead...is this bad for the batteries?

 

[Battery Bum]

I just recently joined CPF after lurking for about a year and apparently I missed this important fact about the reverse charge. Does this effect take place in all devices with multiple cells in series? For instance my wife has three LED "candles" (with 2 cells in series) that she likes to have on 24/7 and I change batteries when one dims or goes out. Is this bad? I also use an FM modulator (2 cells in series)plugged into headset jack for listening to tv, radio etc.. in conjunction with an mp3/fm device around my neck. I have been replacing the set of two AAA in the modulator when it cuts out - which it does abruptly --- it doesn't fade out. My mp3/FM is not an issue (apparently) since it uses only one cell which I replace when it cuts out. It does have a 3 bar battery indicator.
My LED flashlight batteries are replaced when the light dims. Is that OK? We have a digital voice recorder that has the pair of AAA cells changed as soon as the built in indicator shows any weakening. Is that good?
I appreciate any info that will enhance the life of all my cells --- a mix of everything from ROV green and blacks, Titanium Enduro, white top Duraloops, black top Durahybrid, Tenergy R2U (so far pretty impressive for the price - I hope they last), Kodak LSD (fat and run the longest)and some Panasonic 2300mah AA and 780 mah AAA that I have revived from storage for I'm not sure how many years. Codes stamped into the wrapper are 0411 and 0410?

 

[Warhead]

Rather than start a new thread...

What is the lowest voltage I should take an Eneloop down to before recharge?

 

[Mr Happy]

I just recently joined CPF after lurking for about a year and apparently I missed this important fact about the reverse charge. Does this effect take place in all devices with multiple cells in series? ...

I think it depends a bit on the device and the size of the current draw. With electronic devices that have an automatic cut-off on low battery there is nothing much to worry about. Also with low draw devices like remote controls or mice there is probably not much to worry about either. I use a pair of eneloops in a wireless mouse and I just recharge them when the mouse stops working. No problems so far.

The significant danger is with high draw incandescent or powerful LED lights that will drain the batteries into the ground without automatically switching off on low voltage. With these devices you should try to recharge before the light goes dim.

What is the lowest voltage I should take an Eneloop down to before recharge?

With all NiMH cells including eneloops, the guideline for a single cell is 0.9 V under load; with battery packs it is 1.0 V per cell under load, perhaps increasing to 1.1 V per cell when there are many cells per pack.

 

[TakeTheActive]

Unless you are running a single cell device, you should never, never, never run NiMH rechargeable batteries flat. Always recharge them before they show a noticeable drop in output...

...The significant danger is with high draw incandescent or powerful LED lights that will drain the batteries into the ground without automatically switching off on low voltage. With these devices you should try to recharge before the light goes dim...

My only 'flashlight' experience is with 2 cell incandescents (Bright Star, Mag) where it is VERY easy to see when a rechargeable cell (NiCD or NiMH) 'falls off' the plateau - it's as if someone flipped a switch from HIGH to DIM. Do LED lights (Boost / Buck?) react differently? i.e. can you NOT tell that one cell has 'fallen off' the ~1.2VDC plateau visually?

 

[Marduke]

My only 'flashlight' experience is with 2 cell incandescents (Bright Star, Mag) where it is VERY easy to see when a rechargeable cell (NiCD or NiMH) 'falls off' the plateau - it's as if someone flipped a switch from HIGH to DIM. Do LED lights (Boost / Buck?) react differently? i.e. can you NOT tell that one cell has 'fallen off' the ~1.2VDC plateau visually?

That depends on the light, but a well regulated light will stay in regulation for quite a while before it goes into moon mode.

 

[Mr Happy]

It's harder to tell when an LED light is going dim because it doesn't have the same color change from white to yellow that incans have. By the time you have really noticed a drop in output it might be too late.

 

[TakeTheActive]

Unless you are running a single cell device, you should never, never, never run NiMH rechargeable batteries flat...

In a 'mixed company' (Technical & non-Technical) situation such as a forum, I tend to view terms such as FLAT / DEAD / EMPTY as I do WARM / HOT - subjectively.

While *I* understand your "you should never, never, never" reply, IMO, it 'might' be a bit overboard for the non-Technical crowd. For example, my wife regularly hands me her SanDisk 1AAA MP3 player saying "It's dead!". Fortunately, it has a "Low Voltage Shutdown" circuit @ ~1.0VDC. DEAD (UK:FLAT), in my book, is 0VDC!

If I can read at least ~1.0VDC 'Open Circuit' on a cell, I don't feel that I've damaged it. The KEY is to learn HOW DEEP your devices discharge your cells. For example, my HP-215 Digital Camera draws 9.2mA FOREVER when off. If I 'forget' to check / cycle the cells, it *WILL* REVERSE CHARGE them.

 

[TakeTheActive]

That depends on the light, but a well regulated light will stay in regulation for quite a while before it goes into moon mode.

It's harder to tell when an LED light is going dim because it doesn't have the same color change from white to yellow that incans have. By the time you have really noticed a drop in output it might be too late.

Please be more *BLUNT*.

Can a LED flashlight REVERSE CHARGE cells without visual feedback?

 

[Marduke]

In a 2-cell light, it is unlikely but possible. However, with more cells, yes, it is entirely possible.

However, the same can be said for multi-cell incans when numerous cells are involved.

However, it is rather trivial (IMO) to simply recharge often enough to avoid any potential issues, and to assure the best available performance from a light when pressed into service by having the majority of runtime available.

 

[Mr Happy]

Please be more *BLUNT*.

Can a LED flashlight REVERSE CHARGE cells without visual feedback?

Yes, it can. There have been a few reports of the "bulging tailcap" symptom on airtight LED lights, which is a symptom of outgassing from cells due to reverse charging. The people who reported this symptom were apparently oblivious to the fact that their batteries were empty and the light had gone dimmer.

 

[Ozgeardo]

I have been using eneloop AA and AAA's for several years now.
I estimate I have about 50 of each that lurk in all manner of items from household goods, toys, remotes, label makers, flashlights, GPS etc etc.
More often than not I run all these animals until they either shut down or fail to function (Like my GPS) or the performance becomes too poor to be effective (many flashlights and toys).

I have a box where discharged batts live until charged (when I get around to it) and a box of pooled charged batts that could have come from any of my gadgets and possibly have been sitting in the charged box for weeks if not months.

So far I have never had any problems with any eneloops (unlike some other generics that I have experienced).

My Foretrex GPS (I assume is regulated) and my Tactikka XP (unregulated) are my barometers for battery performance (I use them both extensively in the field and know their individual characteristics with run time very very well). If desperate I can recycle my GPS batts into my XP to get some extra run time.

I continually always get about 1 week (16 hours run time) from 1 set of batts in my Foretrex GPS and get 3-4 days (10+ hours, mostly high mode) of use from 1 set of batts in my Tactikka XP.
This performance has not changed in nearly 3+ years since I started using eneloops.

FWIW I believe it is not an issue to let them run down (not to totally kill the batts of course) but I have absolutely no technical qualifications to support this just my anecdotal observations. However I appreciate what some of the technically minded have posted and the more I learn the more I wish I did not know LOL

 

[Turbo DV8]

For instance my wife has three LED "candles" (with 2 cells in series) that she likes to have on 24/7 and I change batteries when one dims or goes out. Is this bad?

We have 4-cell LED candles up and down our hallway that stay on all night. As soon as the first cell drops out, the LED's start a visually noticeable high fequency occilation which rides on top of the normal, slower candle "flicker." Each morning and evening when turning them on and off, I just make a quick visual assessment for this oscillation. Current draw is only about 20 mA, so even if one cell drops out soon after turning it on at night, it hasn't dropped low enough by morning to set up a reverse charge. (I've checked.)

As for remotes, depending on usage, it's not hard to settle on a time period after which you just charge the batteries up before they completely discharge. For example, using LSD cells, if I charge cells in remotes, say, once or twice a year, they haven't discharged completely. It's not terribly inconvenient to charge twice a year. Just jot a reminder down on your calendar, or make it easy to remember, like the turn of each new year.

 

[Swedpat]

Unless you are running a single cell device, you should never, never, never run NiMH rechargeable batteries flat. Always recharge them before they show a noticeable drop in output.

The reason is that if two or more are in series, then the first one to run down is likely to get reverse charged by the others that still have some power left. Doing this repeatedly will seriously damage a battery.

I would like to say that this in most cases isn't possible. I use to recharge when I notice a drop of output, this is the only way I can know when it's time to recharge them. Also in many cases it needs a drop of 30-50% until you react and think: "oh, I think it's dimmer now!"

About NiMh cells I understand that these are not to prefer for use in for example computer keboards, and mice. Not even cycle lights should to be used with NiMh because of the fast drop and risk to run them too low.

My conclusion is: if a brightness drop of the flashlight of 30-50% can damage NiMh batteries, they should not be used in any flashlight without a low voltage protection suited to the actual cells.
I have hard to believe it, because many (non-flashoholic) people regularly use NiMh cells with cheap chargers and they are not even aware of avoiding overdischarge. And the cells still work after long time.
Therefore I suspect that the risk for overdischarge damaging of batteries is A BIT exaggerated?

Regards, Patric