Can i Put these battery packs in parallel

[Ehaze]

Can i Put these battery packs in parallel

https://jag35.com/collections/new-arrivals/products/new-power-cells-battery-pack-14-4v-4-1ahr-59whr-li-ion

If so what is the best way to charge them ? I would like to get the 8.2 ish AH , and i have an I flight 1-4s smart charger that can do 4. ish vs /2 amps max .

[strawberry]

no, each cell should be re/connected (and new battery protection circuit required for twice current)

[NiHaoMike]

You can parallel them if you use a resistor to limit the current during initial connection. Once equalized, they can be directly connected.

[Siwastaja]

Don't parallel pack-level without a strong reason because that requires quite a bit of engineering.

If the balance wires come out directly from the cells, you can do a permanent cell-by-cell paralleling though:

1) Charge both packs to same voltage,
2) Measure every tap on both packs, compare that the respective taps between the two packs are all within about +/- 20mV.
3) Now connect the pack terminals, but also all the taps between the two packs in parallel. Before making each parallel connection, it's a good idea to once more measure voltage between the two wires you have in your hands to verify small voltage difference (< 20mV), right before joining these wires.
4) Make sure all the parallel connections you made are reliable, and that they can't be dismantled easily (no connectors that can be unplugged!)

Now two 4s2p packs have become into one 4s4p pack you can treat as such. It's a permanent solution.

Pluggable/unpluggable parallel packs is a PITA. When you seemingly "want" to do that, usually it works out better to just build a single large enough pack. This is because the parallel connection requires active DC/DC conversion to charge/discharge the packs to the same voltage.

[Ehaze]

ok i guess i will just use them separately on a smaller load ( led light ) .

   They both have bms boards built in so I was going to treat them like a car battery or something  and charge them up , then hook them up parallel using a xt30 and a jht balance lead to the 1 wire , and use my Iflight charger to charge them.
     
          I was think it could make it 2s1p , but i figured i should ask some opinions before i blow myself up

[Siwastaja]

Yeah.

Connecting packs in parallel is equivalent to short-circuiting them. Unless you have equalized the pack voltages close together before, which involves automatic discharging and/or charging.

"BMS" can mean anything. It's never a current-limited constant current supply, it's just protection against damage. In worst case, it's actually not protecting. In best case, the protection works and it prevents catastrophic failure and fire, but it does that by just cutting the current flow, resulting in temporarily or permanently nonfunctional battery.

[Giordano Lanzola]

I built myself a Power Bank using eight 18650 batteries, all without any current limiting circuit.
Overall the PB should be close to 20000 mAh, and I can fully recharge my smartphone three times before it dies.

Apart what has already been said about paralleling, that is absolutely correct, when I first assembled the circuit I remember reading something about Li-ion battery breakdown. It seems that low quality batteries, may sometime experience breakdown.
This is due to the poor insulating structures between internal chemical poles.

Thus if a single battery starts discharging it may (hopefully) go without doing any harm.
However if you have several of them in parallel, all the healthy ones will suddenly start pushing energy into the collapsing battery which will be bearing all the load, possibly exploding or catching fire, which I fear the most.

For that reason I keep the PB assembled just when I need it, and as soon as I'm finished I remove the batteries keeping them disconnected from each other.

As for reassembling I fully charge all the batteries separately and as they all reach the maximum rating (4.3 V) I put them in the PB.

[Siwastaja]

It seems that low quality batteries, may sometime experience breakdown.
This is due to the poor insulating structures between internal chemical poles.

Thus if a single battery starts discharging it may (hopefully) go without doing any harm.
However if you have several of them in parallel, all the healthy ones will suddenly start pushing energy into the collapsing battery which will be bearing all the load, possibly exploding or catching fire, which I fear the most.

This is a very common misconception, but very understandable because it seems to make sense.

But think about it further. If you need certain capacity, the options are:
* Build a larger cell
* Parallel cells

Now the single larger cell would have the same surface area and volume of raw materials as the sum of the paralleled cells, to achieve the same capacity. So the probability of the fault is exactly the same. And, different areas of the cell can still "push energy" into the internal short. So there is no difference.

Except that there is: the smaller the cell, the larger the numbers it's manufactured in. For example, 18650's are easily available from well known manufacturers. Larger format cells are trickier to manufacture and you have to resort to poor quality factories. A larger cell is way more likely to contain a defect, and for an iffy factory, letting that slip through QC is appealing. Having to discard 1% of failed 18650 cells won't totally kill your profit, but if you build 10x bigger cells, you would have to discard 10% of them.

Secondarily, a packaged cell usually has some safety layers beyond what's integrated into the electrodes and separators. For example, 18650 cells come with PTC (polyfuse) and CID (current interruption device, basically overpressure switch) integrated into the cell cap. If the safety mechanisms of the electrodes/separators fail, these cell package level mechanism can still prevent escalation of the issue. This would not work on a single larger cell.

So paralleled cells are likely safer. Li-ion cells are also designed and suppose to be paralleled from day one, so don't be afraid doing that (of course knowing how to do it right.)

But getting genuine cell from the big brand names is most important.