Do I have a problem?

[Vapenstein]

...because I kill an 18650 before the day is done and have to fall back on my 14500 mod. I think I vape too much

 

[mdocod]

What 18650 are you using?

 

[Vapenstein]

some piece of crap that came with my PV, I have some blue Trustfires en route from Deal Extreme, should only be another 3 or 4 months til they get here

 

[Papa Lazarou]

Is that an unmarked piece of crap?

Anyway to answer your question with LR atty's and heavy vaping I can easily drain an 18650 and get well into a second one (various Trustfire) in a day. I never run them down very low - I basically find they've lost a lot of their "oomph" by the time they get to about 3.7-3.8v unloaded voltage.

 

[Vapenstein]

FJO Battery Company currently, generic Chinese

 

[mdocod]

... I basically find they've lost a lot of their "oomph" by the time they get to about 3.7-3.8v unloaded voltage.

That's probably because at 3.7V, the cell is only at about 20% state of charge

3.5V is basically dead, anything below that is dead, from 3.5V to 4.2V open circuit voltage there is a pretty steady correlation from 0 to 100% state of charge.

But WHY would a cell be "dead" if it's still reading over 80% of the voltage that it starts out at? (rhetorical question, read on!)

Think of it like a water tower up in the air. The water pressure at a valve at the base of the water tower is effected by both the elevation of the tower and how full the tank is. The tank can be empty, but the small amount of water in the pipe leading up to the tank is still full and producing nearly as much water pressure as there would be if the tank were full, however, as soon as you turn on the valve, the pipe drains out and there is nothing left. This is similar to what happens at 3.5V on a typical LiCo cell.

 

[Papa Lazarou]

Thanks for the further info mdocod Interesting reading.