Lithium Batteries.

I thought I would give a little advise on how to increase the life of the batteries along with the reasons why. Some of it’s technical but not that much and you can skip over those parts and take note of the effects.

Lithium batteries are used for our electronic cigs and are ideally suited for that purpose. There are however a few things you can do which will improve their useful life. Stay cool, that definitely applies to the batteries. Nothing like an increase in temperature shortens the useful life of the lithium battery. Anything above 25C then the best place for them is in the fridge, keep them with the PI or TI.

The lithium battery does not suffer from memory problems. You don’t have to fully discharge them before topping them back up. However don’t leave them in a discharged state for any length of time.

There is not a microprocessor in them in the true sense of the word but there is a control circuit. This control circuit protects the cell from overheating, over current and over and under voltage and is constantly monitoring the health of the cell. This is why you should not leave the cell in the discharged state; the protection circuit draws current from the cell, even when it is in the discharged state, and should the cell voltage drop much below 2V then the control circuit will not permit the charge cycle to take place, and the only thing you can do is to throw the battery away. (Do it properly, don’t just chuck it in the bin.) Under normal conditions the circuit in the battery will cause the cell to discharge at about 5% per month. So a flat battery could be more than flat in 4 weeks and impossible to charge back up.

The larger the capacity of the cell is the better and the longer it will last between charges.

Yes, this is true but there are also additional benefits which are not so obvious.

The lithium battery has a low internal resistance typically 300mOhms its terminal voltage depends on the actual material used but typically around 3.5V. That is certainly the quoted nominal figure. It also has a certain capacity quoted as 350mA/h or 800mA/h. This means that a 350mA/h cell will provide 350mAmps for an hour, 700mA for 30 minutes or 1.4A for fifteen minutes.

This rate of discharge is expressed in the following way. 1C is the hourly rate, 2C twice the current drain, 3C three times, 4C four times, and so on. Discharge rates over C3 seriously reduce the life of the cell. The normal life of a cell at the quoted 1C discharge rate is around 2 years. We will never achieve that because of the way we use the batteries.

Consider now what we need to heat the 2.4 ohms atomizer.

V/R = I 3.5/2.4 = 1.46Amps

Now think about a 350mA/h cell
     1C 350 mA
      2C 700mA
      3C 1.05A
      4C 1.4 A

1.46 Amps is well over 4C and at that the life of the battery will be considerably shortened by reducing the cell’s capacity.

But for a 700 mA/h cell
      1C 700mA
      2C 1.4A

Well below the 3C rate. So not only will the 700mA/h cell last longer between charges it will also have a considerably longer life.

This 1C 2C rating has to be considered when the atomizer has a lower resistance. A silly little 350mA/h cell will not have a very long life with a 1.2 ohm heater. The drain for a 1.2 ohms atomizer will be almost three amps. In order to remain under 3C you should have a cell which has a capacity of 1000mA/h. Better still 1500mA/h will give you a much longer cell life as well as a longer period between charges.

TW How about producing a simple battery case holding three standard AA rechargeable cells and a small voltage control circuit so that we can select the voltage we require. Not much use for walking around with but as something to use instead of your normal pass through. We could then take advantage of the mass produced battries and their chargers, and we could end up with a 2500mA/h (The highest capacity I have seen to date) battery pack which for the CE2 at 2.4 ohm would remain well below the 1C rating; giving far better battery life as well as longer periods between charging. You would also need to improve the cable entry to the e-Cig as the one I purchased failed there within six weeks.

Another thing which will help with the life of the cell is the point at which you recharge them. As the lithium cell does not have memory problems you can re-charge it when it has only discharged to the half-way point. This will increase the life of the cell and also ensure that the cell voltage never drops below that 2V danger point where the protective circuit will stop it being charged.

Why do we need to stop the cell from charging if the voltage drops below two volts? Simple.

The charging voltage is somewhere between 3.5 and 4V
Subtract the discharged cell voltage and that gives us 1.5 to 2 volts charging potential. The cell has a low internal resistance typically 0.3 ohms which gives us a possible charging current of 5 to 6.5 Amps, the result is heat followed by fire or an explosion. This is one of the important reasons why there is a protection circuit in each battery.

I should give a warning here. So far I have not heard of any cheap e-cig batteries, but I’m sure they are out there. They are for mobile phones. The problem is these cheaper batteries do not contain the protective circuit. High charging currents are therefore possible with the inevitable results. And there is only one possible result, sooner or later. !!BANG!! and one very dead mobile phone. All because they thought they were saving a few pounds or dollars on a replacement battery. This was the reason why some laptop battery packs were recalled, there was nothing wrong with the cells it was the protective circuit that didn’t function correctly.

I hope I have explained it so that you can follow it and not been too technical

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