Lithium-ion battery safety 101

battery voltage under load, or immediately after a load (turbo), is lower than the “at rest” voltage

the battery voltage rebounds after resting

so, when I want to know battery voltage, I reference the “at rest” voltage, not the “at turbo” voltage… :wink:

Running on turbo puts a high current load on the cell which causes the cell voltage to drop as it gets pulled down; when you release the load you will get a bounce-back in the voltage as the cell recovers. This is a normal condition in a good cell. It happens fairly rapidly so you wouldn’t be able to remove the cell quick enough to see the droop on the DMM.

Thanks once again. I don’t have a multimeter so will rely on the Flashlight, however I will ‘assume’ that it is reading 0.1v too high to be on the safe side.

I don’t understand the relationship with volts and amps in a battery yet, but plan on doing more research. I understand that a battery may have a capacity of 5Ah/5000mAh, and that if you use a device that uses for example 5A the battery will last 1 hour before running out of charge, but where Volts fits into this I don’t know.

Looking at the spec of the Samsung 40T I’ve bought the nominal voltage is 3.6V, which is below the 3.7V (half charge) you mentioned. As you can tell I’m a little confused :wink:

> Looking at the spec of the Samsung 40T I’ve bought the nominal voltage is 3.6V, which is below the 3.7V (half charge) you mentioned. As you can tell I’m a little confused

you are learning quickly… I respect your focus and specific question

3.6v is the “nominal” voltage of a LiIon that charges up to about 4.1 to 4.2 volts, hot off the charger

batteries often ship at half charge, and fall below, depending on storage time…

do charge new batteries fully, before use…

Thanks again. So in this example, when fully charged the 40T will have around 4000mAh and 4.2V of charge. If I use it until the flashlight goes out it will have (hypothetically) 0mAh and say 3.0V charge, however it it goes below 2.5V charge this could potentially become dangerous?

For ‘normal’ use I plan on using my flashlight at around 2000 lumens which I believe requires around 6A, which will drain a 4000mAh battery in around 40 mins. My dog walks are around 30-40 mins in a morning meaning that I’m going to take it well below half capacity, nearly until empty. Is this going to be an issue?

> it it goes below 2.5V charge this could potentially become dangerous?

your light will turn itself off before the voltage goes below 2.5V

you do not need to worry about overdischarge, in your light

> I’m going to take it well below half capacity, nearly until empty. Is this going to be an issue?

not a problem… they are made to be used…

your light is safe,
at worst the batteries will run out and you will be left in the dark…

then simply insert a fresh battery, or turn on a backup flashlight…

once you have actual experience, you may find it convenient to lower the output to increase battery life

you may not need 2000 lumens for an hour… you might find 500 lumens sufficient, and get 4 hours

Thanks for all your help. I shall now leave you in peace :wink:

You won’t be able to run 6A with that light for 30 - 40 min. 6A is over 20 Watts at nominal voltage. I wish there were a spec for how many watts a light could dissipate but of course that varies widely depending on the temperature of the environment it is used in and how it is held. In one review the reviewer thought it could sustain 1000 lumen. Whatever the number really is I doubt it will be anywhere near 2000 lumen. If you set out to use it at that level you can feel good and not worry that you will deplete your light in a 40 min walk. Your eyes may not even notice it but unless your walk is really cold I am certain that the current draw will be cut considerably to control the temperature of the light.

> I shall now leave you in peace

pay it forward :+1:

feel free to private message me,
if you would like to brainstorm further, from time to time

I look forward to hearing your results
enjoy the walks :wink:

Are you saying that it will get too hot at 2000 lumens/6A? The reason I thought this would be OK is that a fellow dog walker uses an Exposure Diablo which apparently is 1800 lumens and it only gets slightly warm. Obviously I have nothing to measure that it’s at 1800 lumens and so it could indeed be lower than that but it’s plenty bright enough :+1:

Thanks, will do :+1:

It only gets slightly warm because it has thermal management and that won’t let the light get that hot. 5A 6A for 1800 or 2000 lumen seems in the ballpark. Different LEDs have different efficiency.

Don’t know what light they use and I am not certain how the electronics inside the light will change the output vs the chart linked above. Nearly certain the output would have to be be lower than the chart but not sure how much. The specs for the light pretty much confirm that your friend is not walking around at 1800 lumen the whole time. They list a minimum run time of one hour with a 3500 mAh battery. That would be an average of 3.5 Amps. Looks like you coud get maybe 1400 lumen from that but given the fact that it starts at 1800 Lumen it would be drawing more for some time and therefore must settle down lower than 3.5A. Hopefully someone who understands how an actual flashlight is different from that chart can add to this.

here is a runtime test, to help visualize how different output levels behave:

pic is a link to a review with more details

Wow these things are complicated, whatever happened to just turning a light on and off again lol.

So if I’m understanding this correctly, whilst I might set my flashlight to 2000 lumens (hypothetically) it might only stay there for several mins and then drop down to stop it from overheating? If so is there something in the specs that tells me what the max setting is that it will run at without dropping down (at least for an hour or two)?

P.S. The Astrolux EA01s I’ve ordered is the XHP 50.2 version, I’ve no idea how efficient these are.

Thanks, interesting that if you want any kind of decent runtime it has to be below 1000 lumens. I’ve no idea whether that will be bright enough as my current light ‘claims’ to be 2500 lumens but the fact it runs off 3 x AAA alkaline batteries, and my friend’s Exposure Diablo that claims to be 1800 lumens is much brighter, clearly my current light is not 2500 lumens.


The link in the original post isn’t working and I was wondering what the best way is to ‘store’ batteries when the flashlight is not being used for an extended period of time? For non-protected Li-ion batteries is it best to remove from the light and store in a plastic case, or is it best to leave in the light so that it benefits from the low voltage protection supplied by the flashlight (Anduril). Likewise for a protected battery, I assume for a protected battery its own LVP would protect it regardless?

Any help would be appreciated.

Which link? There are like 80 links in just that post #1

Sorry, the one regarding long term storage.

You may know this already but beam characteristics can make a big difference in the perceived brightness of a flashlight. At the same distances a floody beam has the lumens spread over a wider area. A lower lumen narrower beam can have higher lux and can appear much brighter because the lumens are concentrated in a smaller area.
That can make it hard to judge the lumen output of a light.

Thanks, yeah I appreciate that. After trial and error I’m finding roughly 800-1000 lumens on a flood beam works for us. I’m basing this on my P20ix being 850 lumen in high.