why are people saying 2x18650 mods have twice the run time?

[nic_fix]

I can't find an actual answer. everyone says "lasts forever on 2 batteries". the high wattage box mods with 2x18650 "should" be run in series? therefore the mah should be the same as one battery, not both? of course you are spreading the load across the two, resulting in less amperage per unit I think? maybe a little while longer.

twice as long? please, not speculation. actual answer..

 

[Wraith504]

Connecting them in series will give you more voltage, connecting them in parallel will give you more mah and last longer.

 

[AzPlumber]

I can't find an actual answer. everyone says "lasts forever on 2 batteries". the high wattage box mods with 2x18650 "should" be run in series? therefore the mah should be the same as one battery, not both? of course you are spreading the load across the two, resulting in less amperage per unit I think? maybe a little while longer.

twice as long? please, not speculation. actual answer..

When in series the mAh does not increase but the Wh do.

 

[Dougiestyle]

Parallel doubles the capacity at 3.7v

Series provides double the voltage with the rated capacity (mah) of each cell.

 

[nic_fix]

okay, so all I need to know now is are these mods with two batteries connected in series or parallel? if they are connected in series as I think the claims of "lasts so much longer than single 18650" are unfounded. actually, the ipv3 has a 9v charger so I think that speaks for itself. so much for the claims made about these.

 

[AzPlumber]

okay, so all I need to know now is are these mods with two batteries connected in series or parallel? if they are connected in series as I think the claims of "lasts so much longer than single 18650" are unfounded. actually, the ipv3 has a 9v charger so I think that speaks for itself. so much for the claims made about these.

Well I tried

 

[nic_fix]

that's what I meant. the watt hours increase but it is not double the capacity. at least I doubt it.

 

[Wraith504]

that's what I meant. the watt hours increase but it is not double the capacity. at least I doubt it.

If in parallel the mah does increase so it does almost double the capacity.Not the case in series. in series the voltage is added but the mah/capacity remains the same or takes that of the lower mah rating of the batteries in series.

 

[AzPlumber]

If in parallel the mah does increase so it does almost double the capacity.Not the case in series. in series the voltage is added but the mah/capacity remains the same or takes that of the lower mah rating of the batteries in series.

Wraith, what you're not taking in consideration, at the same wattage the drain on the batteries is less with the higher voltage.

 

[nic_fix]

yes I know this. what I was saying is it is more runtime but not double. people think, two batteries twice the runtime. more but not twice. I would actually like to see someone time it.

 

[Ryedan]

Wraith, what you're not taking in consideration, at the same wattage the drain on the batteries is less with the higher voltage.

This is how I understand it also. This also satisfies my desire that two of the same size and watt hour batteries do twice the work of one. Conservation of energy.

 

[Dampmaskin]

It is very simple. Two batteries hold twice the amount of oomph as one battery.

Any practical deviances from this, are due to differing efficiency factors between different mods, builds, and users.

 

[nic_fix]

I guess I don't understand. 2 batteries in series should not provide twice the runtime of a single of same mah. new math? granted, you get more wh. that is more efficient and will under many circumstances provide more run time. not twice as much. if they were in parallel, indeed that is twice as much mah. it is pretty simple math. of course I could be wrong. maybe they do run twice as long.

 

[Dampmaskin]

Ok, to put it in slightly more scientific terms: Two batteries have twice the amount of stored energy (W) as one battery. Power (P) is energy over time (W/t), so as long as the power (P) output is the same, twice the energy (W) means twice the time (t).

P = W/t.

(Note that the unit for power (P) is Watts (W), and the unit for energy (W) is joules (J); this can be confusing if you're not aware of it. The unit for t (time) is s (seconds).)

Examples:

1 W = 60 J / 60 s.

Double the number of batteries = double the energy. Keep the power constant:

1 W = 120 J / 120 s.

Twice the number of batteries = twice the runtime.

You can also double the number of batteries, and double the power, and achieve the same runtime:

2 W = 120 J / 60 s.

Using joules is probably a bit strange in the context of batteries, but it's simple: 1 Wh = 3600 J (because 1 hour = 3600 seconds).
You can convert between Wh and mAh by using Joule's law: Power (P) = voltage (U) * current (I). For the Lithium batteries that we usually vape with, use the nominal voltage, U = 3.7 V.

 

[nic_fix]

well done. my understanding is the above applies if the batteries are run in parallel. it applies if they are run in series as well? geez if that is true I have been wrong about this for years. I always thought in series will give you twice the voltage but the same capacity.

 

[DaveSignal]

many box mods, especially mechanical ones, are wired in parallel. So, in this case, claims of twice the runtime are accurate.

 

[nic_fix]

true, but I had boxes like the ipv3 in mind when I was asking this. it appears that is run in series. therefore my understanding is it is not twice the capacity. twice the voltage, yes. same mah. splitting the wh should provide some more run time so long as it is not at 150 watts.

 

[AzPlumber]

nic_fix, here is a simple explanation of how this works using two setups, one parallel and one series and both at 10 watts.

Mechanical mod
Parallel (2x2000mAh) 10 watts at 4 volts draws 2.5 amps - Capacity 4000mAh/2500=1.6 hours run time
Series (2x2000mAh) 10 watts at 8 volts draws 1.25 amps - Capacity 2000mAh/1250=1.6 hours run time

Now when using in a regulated mod you factor in
additional amperage drawn when parallel batteries are boosting the voltage
lower amperage drawn when series batteries are bucking voltage

This is just a simple explanation that doesn't factor in regulator efficiency but should help you understand why

 

[Dampmaskin]

Yes, when comparing parallel to serial, some details need to be explicit: Are we talking about unregulated mods? If so, is the resistance of the coil on the serial mod the same as that of the parallel mod, or is it higher?

If the current (and power) is the same, that means the resistance in the dual battery setup must be higher, and the runtime will also be higher. If the resistance is the same, the current (and power) will be higher with serial, and the runtime will not be higher.

If the mod is regulated, is the output power in the one battery setup the same as the output power in the dual battery setup? If so, the runtime should be roughly proportional to the total stored energy in the batteries.

My impression is that most online discussions about this topic ignore these essential questions, and so people talk past each other.

 

[Dougiestyle]

Do not use series batteries in an e-cig mod without a protection circuit!!