Battery maintenance for 100 lumen Wee

I've been wearing my new titanium wee on a necklace for the past month. It gets used for a minute or two per day and I recharge the battery whenever I feel I've used it for 10 minutes or so since this brightest version is meant to run for only 15 minutes or so.

The other day, I went to turn it on and it was very very dim. I checked the voltage on my multimeter and the battery came out at 2.45 volts.

I charged it and it did regain full charge, but I am wondering what is the lower limit that I can safely recharge this battery if I accidentally run it down too far? What voltage is too low for it to be safely recharged?

Don't know the 'official' voltage that it's supposed to be recharged at but I've run mine down so low that it didn't light the LED at all and it still charged up fine. Still using the same cell 6 months later and it's fine.

GOOD TO KNOW THAT!! very usefull information for my new wee ti 100 lumens ( when it comes of course...)

Yucca - Great question!!! I was wondering the same thing...

Jay R - Great answer!!!

Daylight - Congrats! You'll enjoy it!

Mike

Usually, the case with Li-ion cells is that they are permanently destroyed if the voltage ever goes below 3.0 volts. Hot off the charger voltage should be about 4.2v, nominal voltage should be 3.7v and you should be hitting the charger again at about 3.2v

Having said that, I did bring a Wee cell back to life from 2.93v, so it is possible, just unlikely.

MikeSalt said:

Usually, the case with Li-ion cells is that they are permanently destroyed if the voltage ever goes below 3.0 volts. Hot off the charger voltage should be about 4.2v, nominal voltage should be 3.7v and you should be hitting the charger again at about 3.2v

Having said that, I did bring a Wee cell back to life from 2.93v, so it is possible, just unlikely.

Click to expand...

Mike,

I read somewhere in CPF that right when you notice the light dimming, you should try to stop using it. Would that be around 3.2v? I don't have a volt meter to check...I'm thinking I might need to get one...

Thanks,
Mike

Hi YuccaPatrol,

Protected batteries shut off is usually at 2.75v under load. After the load is removed they should bounce back-up to over 3.5v after rest (~30 minutes). Lithium Ion batteries don't have memory, so topping them off is recommended (you don't have to worry about running them down before charging like NiCD). I don't run them down to cut off if I can possibly help it. If you drain them to empty repeatedly, you will get fewer charge cycles.

Charge them up fully and take a volt reading, then let them sit for 30 minutes or so and take another volt reading to see if they are still holding a charge (should be at least ~4.10v).

You may find this chart helpful:Originally Posted by DM51

These figures (below) have been posted before, but it may be useful to repeat them here for those who may not have seen them before. They are the resting voltages of Li-Ion cells with the corresponding state of charge:

4.2 volts = 100%
4.1 volts = ~90%
4.0 volts = ~80%
3.9 volts = ~60%
3.8 volts = ~40%
3.7 volts = ~20%
3.6 volts = empty for practical purposes
<3.5 volts = over-discharged ​

Resting voltage is an accurate indicator of state of charge in Li-Ions. It can be measured when the cell has been resting for ~30 minutes.

Low-voltage protection is set <3.0 volts, to allow for voltage sag while the cell is under load. Ideally, a cell will bounce back up above 3.5 volts after it has been taken off load and allowed to rest, but this depends on the load (current). A small current (light load) will cause less voltage sag, so paradoxically the cell is in more danger of over-discharging if the user are not careful.

You can see from the table above that cells should be recharged before they get as low as 3.5 volts at rest. They can be topped up at any time – this will do no harm, and it is much better than running them too low. I try not to let mine get below ~3.7 volts.

Click to expand...

Cheers,
Steve

Thanks everyone for the great info. Both of my batteries are working fine, even the one that was over-discharged. I'll have to stock up, but for now I am switching them out every day since I probably use the light for 5-10 minutes most days.

MikeSalt said:

Usually, the case with Li-ion cells is that they are permanently destroyed if the voltage ever goes below 3.0 volts. Hot off the charger voltage should be about 4.2v, nominal voltage should be 3.7v and you should be hitting the charger again at about 3.2v

Having said that, I did bring a Wee cell back to life from 2.93v, so it is possible, just unlikely.

Click to expand...

My Ultrafire 123s say the "dead" voltage is 2.75V.