I’m looking for something like shown above, but not for 3xAAA
Where can I buy something similar for 18650 or 20700 or 21700?
3x or 4x.
I assume most if not all are putting the batteries in series. Are there also versions that put the batteries in parallel (with the needed extra electronics to avoid self-draining) included?
That’s what I was looking for! (still looking for 4x18650)
May I as what search term you used.
Even when I search for the full name of the item it doesn’t show up.
Did you try turn off safe search. Because this kind of battery setup isn’t safe to use anyway. 
Couldn’t find 4* holder, best alternative will be to use two 2*holder and stick them back to back. The volume will be the same.
In a distant past when I was still young made a flashlight and put a bunch of 1.5v cells parallel. It worked. But the next day all cells were empty….
If cells don’t have 100% the same voltage they start charging/discharging each other. That’s what I learned back then.
That’s why I wonder why all those battery holders are in parallel. Before I’m really going to use that thing I’ll put charged cells in and check if they are still charged after a week.
Maybe I can mod it to put it in series.
The only reason I want this is for extra capacity, not amps.
BTW I got search working now. The site kept auto translating. Does that count as safe search? 
/EDIT
Those rectangular ones I found up to 8x18650….
It must be round because I want to put them in a host.
Zoomiefan, pretty sure it wasn’t because they charged and discharged each other that caused the batteries to be empty.
If you put multiple cells in parallel the voltage will indeed even out. But it stops when the voltage is equal over all batteries.
Only if a cells is damaged or bad it can happen that the cell will empty the others.
What do you mean by empty? you meant they all had 0 volts when measured with a voltmeter?
Anyways just like thijsco19 said there must have been something else which drained your cells. Maybe some bad parasitic drain or a short or something. All powerbanks you see these days have their cells in parallel, they don’t have any problem maintaining their charge over time.
Extra milli amp hours or extra volts, their energy output will be the same.
* 4x18650 2600mAh in parallel = 3.7V @ 10400mAh = 38.48Whr
When it comes to 4x18650 holder, the cylindrical one and 2*2 flat ones back to back will be the almost same size and volume.
With empty I mean the light no longer worked. Not sure I even had a multimeter back then, when I was 10 yo or so.
I fully agree with your calculations, but that wasn’t what I meant to say. If one cell can deliver 10A peak then 4 cells in parallel can deliver 40A peak. I’m not planing to build a giga-lumens light. Something around 1200 is enough for my use. So a single cell is enough amp wise.
I mentioned in series primarily because of my faulty understanding* that the cells would drain and secondarily it would lower the amount of amps running trough a thin wire. Yeah, I know there are thicker wires (which I have) but when things get really cramped a thinner wire may just be the difference between fit and no fit.
*= When I was a few years older I had a boat with a few big batteries in it. Similar to car batteries. They were in parallel but had a huge diode between them. Always assumed it was for the same reason as my flashlight from 4 decades ago. I Googled for that diode. Let me just summarize my findings as: all the wiring diagrams I found fully support what you and thijsco19 wrote.
I’m gonna order a 4x 18650 rectangular. They are cheap, so why not try
I have put together a number of DIY bike lights that use multiples of 18650 batteries either in series or parallel. You can let them sit of a month or more with no discharge. It’s certainly not batteries wired in parallel that are a problem. I used a number of these cheap Chinese battery holders and discovered there are two kinds, one that comes already wired and usually has spiral springs for the negative pole. The other is not wired and has clips at both ends so you can wire them in series or parallel. This kind holds the battery much more securely so contact is always maintained. I hate the spiral spring type because they often do not maintain contact with the vibrations inherent in cycling. Pictures good for 31 days are here at postimage:
https://s9.postimg.org/8yptasgbj/4_cell_18650_holder.jpg clip type
https://s9.postimg.org/5f3vlj3hb/3_cell_18650_holder.jpg spiral spring type
20 mins ago I ordered the spring type. That will do fine for testing. When I ever have everything ready to go I’ll buy that other battery box. They are dirt cheap.
Clip types are recommended for flat top cells and I prefer them too. Also I find it easier to insert and remove cells from this type of holder.
I had an analog voltmeter and a galvanometer when I was 5 years old. :laughing:
If you want to limit current, then do so using current limiting circuitry, don’t use a thin wire to limit current. What’s going to happen is that the wire will start heating up and you’ll get undesirable results.
I really don’t understand why a diode between batteries? Would make sense if there were 2 diodes or if it were between the battery and the boat motor/circuitry.
How are you going to fit a 4× 18650 rectangular holder inside your host?
