The ups takes 3 x 18650 cells in Parallel - Can I extend to 6 x 18650 safely?

[Chaks]

I need help to extend the runtime of the ups board (see attached image).
This is ups board for a CM4 which has 3 18650 cells in parallel. Can I extend the 3 cells to 6 cells for a longer runtime? by soldering a wire to each of the battery terminal and connecting it to a separate battery case with 6 cells.
Thanks and kind regards,
chaksindia

[stj]

you can.
but a few things to remember:
your charge circuit is the same so it will take longer to charge,
your cells must all match and be balanced when you put them in - so you cant mix-n-match
the more cells you use the faster they will go out of balance and have to be manually balanced.
you do that by charging each of them seperatly so they all have *exactly* the same voltage.

laptops used to use 2 cells in parallel without issies btw.

[Chaks]

So this seems a bit tricky ... I have 6 x 18650 (3000 mAh) in parallel going to the UPS charge circuit which has inbuilt parallel charge circuit for 3 x18650 cells.
if I have to manually balance the other 3 cells in parallel separately then I am stuck.
... Because balancing the cell individually while at the same time they are connected in parallel (and live) to the UPS.
Are there any BMS modules that do this? If so then how to connect it to the same UPS charging +- terminals.

[sam_sam_sam]

So this seems a bit tricky ... I have 6 x 18650 (3000 mAh) in parallel going to the UPS charge circuit which has inbuilt parallel charge circuit for 3 x18650 cells.
if I have to manually balance the other 3 cells in parallel separately then I am stuck.
... Because balancing the cell individually while at the same time they are connected in parallel (and live) to the UPS.
Are there any BMS modules that do this? If so then how to connect it to the same UPS charging +- terminals.

STJ has is correct for the most part but I would also add this

Depending on the BMS protection boards some of them will allow you to use them in parallel but the issue that most of them they do not tell you if can use it in this configuration or not you would have to try it ( meaning that you have three in series to a BMS then another three in series and another BMS board ) the way that you can tell if your BMS protection boards allows this configuration is you have to put a heavy load on both BMS protection boards in parallel and check the output load on both BMS boards are they very close to each other and check the voltage on the individual battery cells and see if the voltage is consistent between battery cells on both BMS protection boards if they are roughly the same on each battery pack then you are good to go with this part but also do the same thing in the charging mode as well you should get the same results if so then the two BMS protection board are compatible with each if you do not get these results do not use them in this configuration look for a different set of BMS protection boards are compatible with each other )

[stj]

another option is to replace the 18650's with 5 o 6 AH 26650's or 26700's
double the capacity with the same number of cells

[sam_sam_sam]

another option is to replace the 18650's with 5 o 6 AH 26650's or 26700's
double the capacity with the same number of cells

I would agree with you the only problem is finding well known brand name manufacturer made in Japan or Taiwan or Korea I would not necessarily use batteries from Canada because there quality is questionable to from my experience 26650 and 26700 it is very hard to find 21700 are also hard to find but you can find Japan made cells

The quality of Chinese made batteries manufacturers are from good quality to very bad quality that I would not even consider using at all I have seen some decent quality made Chinese battery manufacturers but unfortunately because they use so many different manufacturing names it very hard give you any advice on what and how to choose good quality battery from China

But you can tell very quickly if you got bad quality ones versus good quality ones but one other thing I have noticed is that if the only thing on the heat shrink tubing is the battery size and maybe the milliamperes and no manufacturers name you can much figure that they are going be poor quality ones to stay away from

Here is a case in point I had bought a special power tool to install thread rivets and the battery was rated for 2 amp hours but this battery seemed to not last a very long time using the tool and then it sat for several years because the part of the tool broke but the impact tool motor still worked so did the battery pack which I just found it again but the battery was completely dead no voltage at all on all cells

I have had other battery cells that have sat for several years and still have voltage but granted maybe not much but at least a volt or a little bit more and these are Japan made battery cells

[Chaks]

Thanks a lot for all the suggestions ...

The complexity of adding 3 additional 18650 cells in parallel to the UPS has put me off ... as there are too many critical variables to be taken care of and the amount of time/effort required for getting something called stable. To be honest I am scared to take any chances with Charging/Discharging LI-Ion batttery circuits.

My only other option is to get a battery case for 3 x 21700 5Ah cells and pull each parallel connection from the UPS and Connect it to the respective battery terminals. This is the safest I thought.
Genuine 26650 and 26700 are rare or very expensive here in India.

21700 5Ah cells Samsung INR21700-50S 3.6V 5000mAh 9C Li-ion Battery is availabe here in India and costs about 8 USD each so its 24 USD for 3 cells.: Total Capacity :15 Ah
18650 3.5 Ah cells SAMSUNG INR18650-35E 3500mAh (2c) LI-ION BATTERY is availabe here and it costs about 6 USD each so its 18 USD for 3 cells. Total Capacity : 10.5 Ah

I will settle for roughly 50% increase in capacity (10.50 Ah vs 15.00 Ah).

Will the charging circuit designed for 18650's work efficiently with 21700's ?. and more importantly ... safely?.

Thanks
Chaks India

[stj]

the charging circuit only cares about voltage, using bigger batteries just means it takes longer to charge.

[sam_sam_sam]

the charging circuit only cares about voltage, using bigger batteries just means it takes longer to charge.

I would second this the only thing that might happen is if it has a fuel gauge device that tells you how much power left it might not be accurate anymore because of using high amp hour battery capacity so it might show that you are about to run out power but in really there might 1/3 more power than what it is reporting