1

Like many of us, I’ve got flashlights with USB charging functionality and although I like the versatility, I find I still prefer charging the batteries separately.

I like using on-board USB charging but I remove the charge plug as soon as full charge is reached.

What I find I can’t bring myself to do is leave the flashlight still plugged into USB after reaching full charge.

Do they continue to maintain 4.20v and does it speed up the process of cell degeneration?

I can see real value in leaving a flashlight permanently left on USB charge in say the shed or by a back door.

Interested in what others think.

2

Leaving anything charged in runs risk o heating up thus generation possible fires.
I prefer charging externally so you can see what is happening.

3

It should be fine, they usually put no current out once charged, you can check for yerself by using a usb tester ( I have one made by Drok) it will tell you what amps are being drawn & it will give a rough guide on how many mah has been put in.
My iPhone & iPad will show 0 ma current when fully charged ,it also work on my led lenser head torches.

4

Try not to leave the cell charging for long periods. While it will not overcharge obviously, it will reduce cycle life by quite a bit if you leave long times at max charging voltage.

And since lithium ion 18650/21700s self discharge very slowly, it shouldn’t be a problem just leaving the light unplugged for long periods of time.

5

do you mean if you leave it plugged in for a month? yes
But I dont recommend leaving USB, nor regular chargers, plugged in for a month

Li-ion self-discharges about 5 percent in the first 24 hours and then loses 1–2 percent per month; the protection circuit adds another 3 percent per month.

I agree, when my USB charger decides the battery is full it drops to zero, and I unplug it when that happens.
I do not leave batteries on any kind of charger indefinitely.

charging looks like this:

the top numbers gets smaller as the battery fills up

6

Assuming the flashlight has a proper high quality charging circuit in it, the charging should be terminated at 4.2v and it will not begin recharging until it drops below a certain voltage.
Just like your phone or laptop, it will not keep the battery “topped off” at 4.2v constantly, it would only start charging again when it reached 4.1 or something like that.

7

Thanks for the updates …. My confidence is being restored

8

You can’t assume all usb chargers work the same. What specific light do you have? Maybe someone knows if it’s charging circuit powers down or trickle charges, etc…

I know the Eagle Eye X2R shuts down completely so there’s no worries about leaving it plugged in.

9

Most of them use the same IC.
They switch off when charging is complete.
Not sure at what Voltage they switch on again, but they’re safe.

There are also cheap little boars with a buck converter to go from 5 Volts to 4.2 Volts.
Should be much more efficient.
Those boards can do LiFePo too.

10

I don’t ever use the built in chargers.

11

All mine work the same.

You cant assume they dont, unless you test them and find one that does not.

It would be foolish and irresponsible to build a charger that does NOT stop charging when the Cell is full.
.
.

I do check with the USB meter I pictured above.
All my USB chargers shut off completely, including the Olight Universal charger, the USB chargers built into my 16340 cells, the chargers on my 3 different brands of Vaporizers, and the chargers built into my PT16 and PT18, as well as the chargers built into my little 10180 lights (3 different ones).

In fact, I have NEVER seen a charger that does NOT drop to Zero. So YES I can assume they all work the same, and YES I verify that fact also.

12

I stand behind what I said. I’ve read flashlight reviews where they tested the charging circuits and they don’t always turn off completely. Simple as that.

I would always err on the side of caution, not just assume they all work safely. That’s just me, though.

13

The key is quality.
That’s what typically happens in those crappy cheap chinese lights.
I challenge you to find a quality brand-name light (olight, nitecore, etc) that has a charging circuit that does not shut off when full.

14

I use an OLight SR2 Baton ii and am hooked on the magnetic USB charger. It charges overnight every night.

Would there be similar concerns about this type of USB charging as well?

15

i use the built in chargers if the light has one
but i wouldn;t leave it on overnight, just because i probably need the light, that was why it ran down, i used it and need it again soon

as far as trickle charging, there is no way to guess what any charger does other than read its docs or test it

they might let it run down to 4.10V, or 4.19, or 4.1999, before charging it back up

external chargers may or may not do that, also
i have 2 that trickle charge and one that does not - ever - i think it is the liitokala

i like trickle for nimh cells like camera batteries. they can have a lot of self discharge, and the cameras are very picky about cell voltage
it isn;t as necessary for li ion

wle

16

USB Charging is definitely NOT a feature I look for in a light. If it happens to have USB Charging & I like the light, I will go ahead & buy it IF the USB plug is securely covered or if it has a substantial rubber plug/cover for the USB plug.

As far as using the USB Charging. I do use it on occasion but I DO NOT leave the light plugged in after charging is complete.

As well as Rechargable LiIon batteries retain their charge, besides the obvious ’possible’ hazards of leaving the light plugged in; I see no need to do so.

my .039…… :wink:

17

Olight R50 Seeker Pro. When leaving it on the dock, it is known to ruin the battery after a few months.

18

I don’t think we are talking about the same thing here.
.
I’m talking about when the flashlight finishes charging you can leave it for hours or a day on the charger with no issue, just like plugging your phone in at night.
It will obviously finish charging in a couple hours but it is perfectly safe to leave it plugged in and unplug it in the morning.
The charging circuitry shuts off when the capacity is filled, you don’t need to “babysit” the phone/flashlight/device and unplug it immediately when it terminates.
.
Leaving a device plugged into a charger permanently for months at a time is a completely different matter.
No flashlight manufacturer recommends you do that.
I have contacted both led lenser and nitecore and both have always told me to not store my flashlight plugged into the charger/dock.

19

they will all shut off when full, otherwise the ‘deterioriation’ would be very fast.

the issue is what happens later, after a little discharge, do they charge it back up to 100.00000% full or let it run down slowly
?

wle

20

It depends on the circuitry.
Some will not start charging again until they are unplugged and replugged (the safest option IMO).
Some will start charging once it reaches a certain threshold voltage.

Then there’s the crappy “charging” flashlights that simply apply 4.2v constantly and never stop trickle charging, killing the cells.