Yes, the riskiest is when you put a deadish battery inline with a full one. The full one attempts to charge the dead one in reverse when the circuit is complete and it goes into failure.
CFP completes exaggerates the risk in general. LiCo's are "dangerous" but so is the gasoline in your car. Just use due diligence when handling both.
I had the same question as this thread. I use a Solarforce L2M mini with a 18350 rechargeable Li-ion battery. I usually can see when the power is low, around 3.60v and recharge the battery. But sometimes the battery is at 4.12v and I just pop it back into the charger. Good to know it does not shorten the life or damage the battery.
Has anyone had any problems with rechargeable li-ion batteries that are shipped air freight or taken on board during a plane flight. I usually have trouble with any NiMh batteries that travel by air. I wonder if I will have the same trouble with Li-ions.
Asking about airplanes and batteries sometimes causes feelings to get hurt, but I put 2 batteries and a sweet flashlight thru the x-ray scanner @ Washington international on Dec 23 without incident, and had another 4 in my checked luggage that didn’t get stolen.
Carrying an item on a plane is really about your attitude.
LI-ION has the best life at less then 80% charge.
Charge to 4.1 recharge at 3.7.
Don’t store at 4.2 store at 3.7.
Cycles don’t don’t hurt them but OC and running them dead does.
Experts can help here.
How would one go about getting 3.7V? The chargers I have experience with do not have a charge to or discharge to any selectable voltage. Are you manually monitoring the charger or doing manual discharges?
This is correct.
Is it practical? No.
Worth the time and equipment investment to get 20-to-50 % more cycles before getting 70% of stated capacity? You decide.
I don’t have that much spare time, and if I had I’d do other things.
Refresh cycles will give you peace of mind: invest 40$ in an opus BT3100 and relax.
@Mike C In a “hobby charger” you can set the voltage of what a lithium chargin program should be.
Also my REAKTOR, has a function that’s called “Lithium STORAGE” which allows you to charge batteries to 3.7V
Hoby charger are great chargers, once you start to discover how many things and situations they can handle you pass on the disadvantages of having a mess of cables, clamps, and other DIY stuff.
Also I suggest keeping a battery or more, depending of which torch do you plan to use in that case, for emergency, they will be a bit more abused than others batteries, but better safe than sorry.
In the case you have a “programmed” emergency, meaning you have 1 hour or so to charge some batteries, with an hobby charger you could pull something like 10A in a parallel of 4 IMRs and charge them all in something near 30-40 minutes
Thanks, I might have to look into using a hobby charger some day. I’d probably be happier if say the Opus or other analyzing chargers had the storage option though.
It does, you just have to open the case up to get at the switch.
I’ve never had issues with taking li-on batteries on domestic or international flights. On my last trip to Africa I was carrying all our lights and batteries, as well as some I was giving away. I had 2 18650 lights with the batteries in them, another 4 18650’s in plastic containers, and 16 NiMh batteries. Nary a comment or second glance from TSA or the Ugandan security folks when flying back from there. That’s always been my experience when flying with many batteries.
Aha, thanks! For some reason I thought it was only 4.2 and 4.35.
Li-ion batteries age faster if they are stored fully charged or fully discharged. It is best to store them cool at around 3.6V - 3.7V.
So it is best to only charge if the battery is below say 3.3 volts.
But all that happens if you top off your batteries before that is that they age a little faster. You will loose capacity a little faster. But I suspect that most prefer to have flashlights with fully charged batteries to having slightly longer life on the cells.
I charge all my eneloop Ni-MH at least once a year by rotating all of them. Ni-MH likes to be stored fully charged better than Li-ion.
I store my spare Li-ion at 3.7 volts in a dry and cool cellar, and check them once a year. I have just a few Li-ion cells in use that I keep topped up. So I rotate as few Li-ion as possible to be able to store spares at 3.7 volts.
If there is an extreme emergency and I need more cells charged, I have a charger that runs on the battery of a car, so I can charge my spare cells that way.
Adoby’s one is a good compromise usage, in that it is both practical (having some cells always filled up and ready) and easy on the batteries stash, since most of them are properly stored. The backup 12v charger is a good idea to face emergencies in which there’s no access to grid, I have 4 chargers working that way and an inverter too for that reason.
I do just as Adoby does.
BTW most of voltage drop happens in the first year of storage if I recall correctly, so if you stored some batteries topped off a while ago, just leave them be and they won’t be too hurt.
Where? I’ve only heard of the 4.35v switch. I do have and Opus and use it extensively.
FWIW I do have a hobby charge and do put my cells not being used at storage voltage. Some people here have dozens……(and dozens) so for that kind of stash you may as well.
I agree with the process Adoby (post #31) uses.
Thanks. Did open it up when new to grease the fan but wasn’t looking for that so didn’t see it.
Useful but not handy. 
I asked about batteries on planes primarily because I have had an almost universally bad experience when I shipped Ni-MH batteries by air. Almost all the bateries eventually started to leak. (this was a while ago.) So I was concerned if I took Li-ion batteries on a plane I might also get leakage.
But since posting my question I read on the Fast Tech website that they are now able to ship batteries by air using Sweden Post. If this is true then many other Chinese firms will also start shipping batteries and we may get a flood of good cheap batteries. I am concerned if they might start to leak as well.
This sounded easy, but it doesn’t appear to be as easy as I would have assumed. I’ve now got the Opus 3100 and have done some capacity tests on cells that are in storage. First I charged them full with the switch on 4.2V. Then I did the discharge test to get an approximate capacity reading (discharge current 1A). The cells discharged giving me readings I would expect from these cells, maybe slightly lower in some cases, and the charger appears to discharge them down to around 3 to 3.2V before stopping (according to the display on the charger).
The thing is that after the discharge, the cells voltage rather quickly bounces back up to about 3.7V, so when I put them in the charger with the switch on 3.7V the charger either says full, or just charges a very small amount of mA. What’s going on here? As far as I have read, storing depleted cells is bad for them. Are my cells depleted after the discharge, and depletion voltage in resting state is about 3.7V, or has the Opus charger not fully depleted them during discharge? Charger reported mostly above 2000mA after discharge. Should I charge them with say 500mA before storing? Or is storing them at 3.7V after the Opus discharge OK?
Yes, that’s the correct way.