Vape and charge at once

[Bdbodger]

If you had 2 li ion 3.7v batteries in series and also had one of these 7.v chargers Your Mega Battery Source For 7.4 Volt Li-Ion / Li-Po Battery Pack Smart Charger
could you charge and vape at the same time like a passthough or would you need a special circuit or swithch .

 

[Dalton63841]

It is designed for 2 cell battery packs, and if I recall correctly those battery packs have the electronics inside to ensure each battery gets the proper charge. This is necessary with batteries in series. So in other words you would probably still need a charging circuit.

 

[Bdbodger]

Well still not sure about that . The batteries are protected 18650 batteries and the charger has " Built in IC to cut off power automatically when battery is fully charge

Red Led will show Battery while charging and Green LED shows full."

I will have to look more into how battery packs are made .

 

[bstedh]

"Proper" Battery packs have a circuit built into them the ensures that the cells charge and discharge at an even rate. The big thing that you want to avoid is imbalance. Both cells need to be equally charged. This is less of a problem with series but it is still important.

As an example when using two batteries in series the cell closest to the negative terminal will discharge lower than the other. The big problem with charging in series is that you have no control other than the batteries internal PCB "if you are using protected cells" to keep an individual cell from going over 4.2V. You could easily have one go over voltage fairly quickly charging them in series. And if the battery protection cuts off the charging in one cell that means the other isn't fully charged increasing the discharge imbalance.

Another thing to keep in mind is to never ever ever take a couple of batteries that have been used in series and put them directly into a parallel configuration without charging them first. Also with any multi battery setup, always allow the cells to fully charge prior to use. That is one of the reasons it is always recommended to keep batteries in matched pairs. If batteries are stored for any length of time you should top them off prior to using.

 

[WillyB]

...Another thing to keep in mind is to never ever ever take a couple of batteries that have been used in series and put them directly into a parallel configuration without charging them first. Also with any multi battery setup, always allow the cells to fully charge prior to use. That is one of the reasons it is always recommended to keep batteries in matched pairs. If batteries are stored for any length of time you should top them off prior to using.

And why is that?

I just took a partially discharged cell ~3.9V and paralleled it with one at 4.21V. Only did some very light vaping, but an hour later they were both at ~4.03V. And when I finally pulled them for recharging, again identical @ ~3.4V.

it is always recommended to keep batteries in matched pairs.

Has anyone actually bought 'matched pairs'? No one I've seen offers them and I don't have the equipment, or energy to actually match them. And when in series, seeing as they discharge at different rates (it's not uncommon to trip the protection circuit of one of the cells), they will basically age at different rates which further un-matches them.

 

[bstedh]

What I mean by matched set is that the batteries are kept as close as possible in age, use, and charge level. This requires a level of monitoring that most will not follow and for a large part I do not either. It is better to have safe information to guide the method that you do chose to follow.

My understanding is that when you put two batteries in parallel the voltage difference tries to even out and the amperage that shoots between the two cells is extremely high due to the low internal resistance of the cells and this is what can lead to failure. The amperage levels can reach almost as high as you would get by shorting the cells.

The internal protection of the batteries may buffer this with good quality batteries but it's not something I prefer to completely trust. Best practice is the safest method. I personally recommend treating all cells as if they have no protection circuit because it can fail on you and the more you abuse them the more likely it is they will fail. I have been repairing electronic devices for almost 30 years and I can tell you that a lot of electronics will just fail for not good reason where others will keep going even though they have been abused well beyond their spec'ed tolerances.

I will say that I am by no means an expert on batteries and most of what I do know is from the internet and this forum so I could very well be wrong in some of my assumptions.

 

[CraigHB]

I would agree with everything you've said bstedh. If someone doesn't buy warnings like this, it's certainly their perrogative to do what they want. However, it's better to take some simple precautions than find things out the hard way. I've discovered plenty of things in electrical and electronic work the hard way and I've never said I wish I had been more careless.