Lithium batterys explained(ish)

[Crossbow]

Credits first - most information, and all the graphs were from http://www.mpoweruk.com/

As most of you already know, Ecigs use Lithium - ion batteries. The main reason for this is the high voltage, the way in which they discharge and their high energy density (a small battery holds a lot of power)



As you can see, after an initial steepish drop, discharge voltage remains fairly steady, up until the end, where it plummets.
Lithium batteries also hold charge well - most rechargeable batteries will self discharge in an annoyingly short period of time, typical self discharge rates for common rechargeable cells are
    * Lead Acid 4% to 6% per month
    * Nickel Cadmium 15% to 20% per month
    * Nickel Metal Hydride 30% per month
    * Lithium 2% to 3% per month
This isn't quite the whole picture however - most rechargeable batteries only have reversible self discharge - Lithium batteries actually permanently lose capacity over time! This is why ecig batteries are relatively short life items
The rate of this loss is largely temperature based.... bad news for hot titans!




The rate a battery is discharged at also affects its capacity. This is expressed as a C - rate, with 1C being a one hour discharge time, so a battery discharges in an hour at 1C, 30 mins at 2C and 2 hours at 0.5C. High discharge rates significant damage battery life, bad news for Uber heavy users like me.






The same C rates, and their effects apply to charging (to some extent, and to keep it simple) which is why most chargers take several hours.

Lithium battery chargers are generally constant current - constant voltage, where initially a constant current is applied (resulting in an increasing battery voltage) which is then switched to constant voltage when the voltage reaches 4.2V (as overcharging lithium batteries is BAD)





Its also possible (and I haven't checked, but I imagine this is how ecig chargers work) to charge using constant current ONLY. In this case, charging stops at the end of the flat green part of the graph above. This reduces the capacity of the battery to about 80%, but simplifies the charger and usually slightly extends battery life, and of course reduces charge time

Most commercially sold Li batteries have a protection circuit (and that includes all ecig batteries) which does 2 things - it prevents an input voltage of more than 4.2V being applied (to prevent the likes of this happening) and to prevent it being discharged too far - if the cell voltage drops too far, the chemical reaction becomes irreversible, and the battery wont hold much if any charge.
Some of the larger Lis (such as 14500 and 18650) may, or may not be protected - if they aren't it's vitally important to use a protected charger!

[spiraller]

Fantastic information cross, I'm making this a sticky and referencing it in the FAQ! Hope that's okay

[Crossbow]

Of course

[SludgeVanDiesel]

I wish I was more technical.

[~K~]

Cross lost me lmao as that is to tech for me 

[moog]

I wish I was more technical.

LOL..Same here....

[Crossbow]

I wish I was more technical.

Me too

[prof beard]

On the subject of "unprotected batteries" - these are NOT lethal man-killing devices (as some on the dark side would have it) PROVIDED (as has been said) a proper charger is used.  It is also preferable to use a slow charger rather than a fast one for these batteries.  The SD uses unprotected batteries and (as trog has said) you "could" overcharge them with the wrong chargers - however he has also said that there is no realistic likelihood of someone dangerously depleting such a battery in an e-cig as the atomiser stops working before a dangerous level of battery flatness is reached

[IYFZZZ]

If the rate of loss is largely a  temperature issue then why encase the batteries  in a solid round casing? In my field of expertise when you have a heat sensitive item you would not use a flat surface ( I know the ecig is a round cylinder) but by adding very small ridges you create more surface area hence more heat can be dissipated quicker.  The ridges also take the heat away from the body of the battery this would also help.

[Crossbow]

Most of ecig design is based around the cigarette look, and of course, having a metal body and connector provides heat conduction between the atomiser and battery. Its the heat from the atomiser thats the issue - unless a battery is already FUBAR, it shouldn't generate significant internal heat.
That said, on a small battery, the biggest issue is likely to be charge and discharge rates, atomisers can draw anything upto 1000mA, which is about a 5C discharge rate. Its intermittent, so its not as bad as constant discharge, but its not going to help matters.

[Larry]

I notice these e-cigs are consumable so people have to replace batteries and atomizers.  That seems wrong to me.  If I could unscrew the tip and drop in a couple of AAA batteries I'd be happy but what's with the atomizer burning out?  Maybe someone will make one that has an indefinate lifespan.

[Angela]

I agree Larry, but unfortunately it seems to be going the other way with disposable 'cartomisers' (a combined atty and cart).  I will resist that at all costs!

[Crossbow]

Thats one of the reasons I bought the Janty Stick Replacement batts for £2.50.... hell yeah!

[moog]

or even cheaper at dealextreme....

[g-grandad]

Is there something in the design of lithium batteries that limits their capacity ? AAA NiMH rechargeable batteries are available at 1000mAh these days.

[Crossbow]

In theory, the newest NiMH have about the same energy density as Li-ion, so they should be comparable sizes, I think that cost is probably the limiting factor for Li capacities, as Li is about 4 times more expensive (and thats the industry cost). As has happened with NiMH, larger capacity Li batteries will probably start appearing as price drops

[FireSprite]

Is there something in the design of lithium batteries that limits their capacity ? AAA NiMH rechargeable batteries are available at 1000mAh these days.

Ah but lithium batteries have 3 times the voltage of NiMH. A battery's energy is measured in mWh and to get that you multiply the mAh by the volts. So a 1000mAh NiMH (1.2V) has 1000 x 1.2 = 1200 mWh, and a 360mAh lithium (3.7V) has 360 x 3.7 = 1332 mWh.

[moog]

Welcome to the forum Firesprite...

[~K~]

Welcome to the forum Firesprite 

[Larry]

Totally Wicked is selling a 5 pack of batteries and atomizers for both the 901 and the Titan.  I don't need batteries right now but I will in the near future I think so if I bought the 5 packe and kept them fully charged but didn't used them at all, would they degrade on their own and eventually become usless or would I be better off buying them as I need them?

[Crossbow]

if I bought the 5 packe and kept them fully charged but didn't used them at all, would they degrade on their own and eventually become usless

The best answer I can give to that is... kinda
Lithium batteries (apparently) store best if less than fully charged, and if stored cool, don't drop off terribly fast - if you have a look at this graph...

You can see that a battery at about 20 deg C will lose about 10% of its capacity in 12 weeks - not exactly a huge problem.
Based on what I know (and I'm no expert) I'd say that if you part charge them after testing (give them 10 mins or so each) and store them cool, the money you save will far outweigh the capacity loss

[prof beard]

As far as I'm aware all e-cigs use lithium batteries

[moog]

Cheemiss...checkout our FAQ section at the top of the forum.....click....most of what you need will be there....welcome to the forum...

[Crossbow]

Cheemiss...checkout our FAQ section at the top of the forum.....click....most of what you need will be there....welcome to the forum...

ALways a good start - and if you haven't already ordered, don't
Bear in mind that a company that employs sales reps will almost alwys be more expensive than one that sells direct. Also bear in mind that there arent actually that many models of E-cig, so theres a very good chance that any brand name is available elsewhere, and often much much cheaper.

As fas your question goes - any cigarette shaped E-cig will have a battery not significantly different to any other (other than disposable ones), they're much the same.

[MrMylesGuy]

So is it possible to say... take apart a titan battery and drop in say a new AAA? 

I think if e-cigs are goign to catch on they can't be this disposable.  Something dies I have to wait for my order to come online, I can't just pop in a new battery. What is it about atomizers that kills them?  They are just metal heating up.  Seems like there should be an easy fix. I realize these companies probably want you to keep buying from them, but I would much rather pay a premium for a replaceable AAA rechargable and a long lasting atomizer.

[Larry]

 I'm afraid an AAA battery won't be able to power the atomizer, in fact, not even two of them will because that would only be 3 volts total and the batteries with our cigs are like 4.1 volts at a full charge.  Three AAA batteries would give you 4.5 volts which might be too much so you might need to add an inline resistor to cut the voltage down a little before the atomizer.
The coil in the atomizer is thin so the low voltage of 3.6 to 4.1 can work with them.  If the coil was any thicker, You'd need higher voltage to heat it up and get vapor from it which means you'd be carrying around a bigger battery  You can fashion an atomizer that would last for years if you plan on hooking up to a car battery.  Look at an electric burner on a stove and how thick the ni-chrome is.  Yes they last for years but they're thick and have to be plugged into a wall outlet to work.  Not even a car battery would last long with a draw that great. 

[DaveDzRochNY]

Lithium batteries (apparently) store best if less than fully charged...

OK, so...

Say Somebody buys a HUGE stash of batteries and they arrive partially charged.
Should Somebody deplete the charge (down to flash mode) before storing them
away and then bring them into use only as needed when old ones bite The Big One?

Signed,
Somebody

[Crossbow]

Say Somebody buys a HUGE stash of batteries and they arrive partially charged.
Should Somebody deplete the charge (down to flash mode) before storing them
away and then bring them into use only as needed when old ones bite The Big One?

Nope, best to leave them part charged, otherwise they may tip over into 'too flat' while they are stored, and you have a huge stockpile of metal cylinders

I would much rather pay a premium for a replaceable AAA rechargable and a long lasting atomizer.

Try a Janty stick (it takes cheap 10440 batteries) and combine it with a 5 pack of 801 atomisers from TW. 801 atts are pretty reliable, and 5 ought to last a loooong time

[jonuk76]

Hi Crossbow, do you (or anyone else for that matter) know much about the difference between Li-Ion and LiFEPO4 batteries, and their respective chargers?  LiFePO4 (Lithium Iron Phosphate) batteries are apparently much safer than Li-Ion's. They don't have a tendency to explode or catch fire.  They also have longer service life, but on the downside don't hold as much power as Li-Ion's.

I recently got some Tenergy LiFePO4 3v protected batteries which came with a specific charger for them.  I also ordered some spare 3v Li-Ion batteries (1000 mah rated CR123A's) from DealExtreme. I assumed at the time I'd be able to charge them with the Tenergy charger, but now I'm not sure. I'm a bit wary of trying it and seeing... Any thoughts?

[Crossbow]

My (quite possibly flawed) understanding is that LiPo are much safer, but the chargers aren't compatible - I'm not sure why, especially in the case of batteries with the same voltage (and it's too far past beer oclock to research it now )