Issues with KangerTech Subox and/or efest batteries

[nyiddle]

Hello I'm EBates and I am a Tootle Puffer. I vape my DNA30 and DNA50 Boxes at 7 watts and my KF's sport a 2.5 ohm coil.
I have used a set of 4 Panny 18650PF's for over a year now ( the 4 are used in rotation) using the 'Low Voltage' warning of my dna's to tell me when I need to swap batteries (supposedly low voltage is ~3.2vdc, but I've never checked). My point being that a decent battery should last a lot more than 6-7 months and discharging below 3.5 or what ever voltage, IME, has had no effect.
Mechanical mods are a different story but regulated mods, I stop when the mod says stop with no ill effects (to this point).

Personally, I think recharging at 3.5/3.6 volts and not letting the battery drop below that is overkill. When the mod cuts off at or just below 3.2 volts, it is still well above the minimum voltage. For example, the Orbtronics SX30 battery has a minimum discharge battery voltage of 2.5 volts. This means at 2.5 volts, the battery is essentially fully discharged (and fully discharging will potentially damage your battery). The Sony VTC5 has a minimum voltage of 2.7 volts. The Samsung 25R and the LG HE4/HE2 all have minimum voltage ratings of 2.5 volts.

So what this really means is that if you let the battery voltage fall to 3.2 volts before recharging, you are really only using 60 percent of the battery capacity and are recharging it at 40 percent (assuming that the battery drop is linear).

The consensus among many battery experts (both in and out of the contexts of vaping) is that charging your high-drain Li batteries at around 3.4/3.5V is a good habit, and will likely increase battery lifespan by a fair amount. I'm not saying you'll find yourself in a catastrophic mess if you do otherwise, but it's not asking much for me to charge at 50% on my Sig150. With 2x 18650's I can easily vape from 9am-9pm before getting down to about 50%.

And for the record, while the "minimum discharge voltage" is around 2.5/2.7V for most batteries, if you try and vape at that low of a voltage you're almost guaranteed to do some damage to your battery, or potentially your regulated device. You never want to fully discharge your 18650 batteries. Ever.

 

[Gahh]

The way I look at it, with the 3.6 volt cutoff, the Subox only uses about half of the capacity of the battery. As a comparison, if I use the battery in my SX Mini all the way until the battery no longer fires the mod, when I put the battery in the charger the voltage reads a little under 3.2 volts. With a nominal voltage of 3.7 volts and a maximum of 4.2, this means that the SX Mini is using all of the available capacity of the battery without damaging the battery.

Good thing for me to know when I get my Kt. Subox.
Thanks for the heads up.

 

[Mooch]

On the contrary, I don't recommend discharging your batteries much lower than 3.5V. In fact, the higher nominal voltage you can charge your batteries at, the longer their lifespan.

For this reason I don't discharge my batteries farther than 50% on my Sigelei 150, because at 10% (when the device stops firing) the battery's voltage is 3.2V. Too low.

While never discharging below 3.5V might extend the cycle life a small amount, IMHO it's not worth the loss in run time each time you use the cell. These cells are spec'd to have a decent cycle life when discharged down to 2.5V-2.75V. Stopping at 3.2V or so will increase your cycle life a good amount but stopping at any voltages above this really doesn't add any more to that cycle life.

But, having said that, it someone is OK with charging the cells more often (to only 4.1V I hope!) then it certainly won't hurt.

 

[Mooch]

The consensus among many battery experts (both in and out of the contexts of vaping) is that charging your high-drain Li batteries at around 3.4/3.5V is a good habit, and will likely increase battery lifespan by a fair amount. I'm not saying you'll find yourself in a catastrophic mess if you do otherwise, but it's not asking much for me to charge at 50% on my Sig150. With 2x 18650's I can easily vape from 9am-9pm before getting down to about 50%.

And for the record, while the "minimum discharge voltage" is around 2.5/2.7V for most batteries, if you try and vape at that low of a voltage you're almost guaranteed to do some damage to your battery, or potentially your regulated device. You never want to fully discharge your 18650 batteries. Ever.

I think that's due more to the increased current draw at low cell voltages, in a regulated mod, than the discharge cutoff being close to the spec'd minimum. High temperatures are a real cell killer.

Discharging down to only 3.4V-3.5V is a good recommendation and one I might also make since it provides a safety buffer for possible overdischarges, accidents, and excessive current draw at lower battery voltages in a regulated mod. But in my experience it doesn't provide any benefit over going down to 3.0V-3.2V...unless you really pushing the cells crazy hard and the lower discharge voltage means that they more time to heat up and damage the cell. But that means you are using the wrong cell, not that the 3.2V discharge inherently causes more damage than 3.4V-3.5V.

 

[Boden]

The mod is not measuring resting (unloaded) voltage it is measuring voltage under load ie. sag. If the battery comes out of a mod and measures ~3.5V it is at ~3.2V under load. If it measures 3.2V with a multimeter the mod is cutting off at ~2.7V.

 

[MattMo81]

Found the culprit for my issue with the Subox. My old batteries. Bought a brand new samsung 18650 today and i've been vaping like a champ ever since i popped it in. Guess I'll use the old ones on my old Kbox, since they still work fine on my Nano. Thanks for all the input. My next obstacle will be re-building a coil on the RBA. I'm sure I'll be back. Have a great 4th of July everybody

 

[Mooch]

The mod is not measuring resting (unloaded) voltage it is measuring voltage under load ie. sag. If the battery comes out of a mod and measures ~3.5V it is at ~3.2V under load. If it measures 3.2V with a multimeter the mod is cutting off at ~2.7V.

There will definitely be a difference between the voltage you measure and the loaded cell voltage but it's going to vary a lot depending on how hard the cell was being run and the time between your last hit and when you measure the voltage. Good point though!