Are 18650 and 21700 batteries electrically similar?

Batteries and Chargers Rechargeable Batteries
1

I am unsure if I can charge my new 21700 Molicell flat top batteries,which are on order in my ‘old’ Nitecore IntelliCharger 2nd Generation i4 Battery Charger.
From what I can tell(being a newbie),21700 and 18650’s are basically the ‘same’ electrically,other than the obvious physical size and capacity,both are 3.7-4.2 volts,so my main question is if these new 21700 batteries can be charged in my ‘old’ Nitecore IntelliCharger 4 bay charger which came out before 21700 were available,as long as they will physically fit in the charger.ThanksHB

2

Yes, but be sure that they fit first.

I put a 21700 in a charger that wasn't big enough, and I ruined that 21700 and one of the channels of that charger.

I felt like an idiot for quite a while after that incident.

3

Thanks for posting. I am trying to learn a little here,so how did you “ruin that 21700 and one of the channels of that charger”?….did you forcefully try to install the longer battery into the shorter position of the charger? Thanks again! HB

4

Here's a thread that I created about my experience:

https://budgetlightforum.com/t/-/62879

I believe the cell short circuited.

5

Very interesting thread.So,from what I don’t think I understand,the charger should be powered up(usually what I do first)or it doesn’t matter before installing the batt(s)?
These are the batts I just bought and waiting on… Molicel 21700 P42A 4200mAh 45A (Flat Top High Drain Battery) – E-CIGARETTES.CA INC. Thanks, HB.

6

No.

Like I said before, you just have to make sure that the cell will fit in the charger before you insert it.

According to https://lygte-info.dk/info/roundCellChargerIndex%20Universal%20UK.html

and https://lygte-info.dk/review/Review%20Charger%20Nitecore%20Intellicharger%20new%20i4%202017%20UK.html

...your charger only accepts cells up to 70mm long.

Your cells are Dimensions: 70.20 mm (Max) x 21.70 mm (Max)

I wouldn't try to insert a 21700 cell in that charger, but the choice is yours.

The cell will either just barely fit, or it might short circuit like mine did.

The safe thing to do is to get a charger that is made for a 21700 cell.

7

No. What you should do before you use it it is read the instructions and the spec sheet to determine what kind of batteries the charger can accommodate.

If you do try and insert it, if you feel some resistance , back off , don’t force it.

8

That’s the ‘thing’,my charger came out before 21700 batteries were available,so that particular charger won’t list in the manual/packaging that those batteries (21700)as being ‘acceptable’ for this charger.
Thanks,HB

9

Thanks,HB

10

I just received my new 21700 flat top batteries and they do in fact fit into my ‘old’ Nitecore IntelliCharger i4,with a bit of room to spare,maybe .020,but button tops would likely not go in.At least I don’t have to buy a new charger! Thanks to all who commented.HB

11

Great to hear!

I really didn't think that they would fit, but I'm glad to be wrong.

12

Yeah,I had my doubts also! Thanks,HB :+1:

13

Just be careful inserting them in the charger — the whole battery shell is the Negative, even the top edges surrounding the positive contact —- so if you tear that shrink wrap on the top edge putting it in the charger it makes a direct short —- Bad Bad Bad

14

same but the bigger one will take longer to charge [maybe]

15

Thanks,HB