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Need help designing 18650 battery pack. Answered

Hey guys, I'm trying to transform my JBL iPod deck which uses 13v 2.5Amps into a wireless bluetooth speaker for a better use. I have a couple of 18650s which has a capacity of 2500mah so i tried to connect 6 batteries in series and got 12.8volts but the issue is the battery capacity doesn't increases. Also some of the battery are 2.3v and 2.89v when fully discharged and has voltage of 3.6v as usual. So my doubt is can i connect 3x2.3v + 2x2.89v battery in series and 3x2.3v and 2x2.89v battery in parallel with the series ones to make it achieve more battery capacity?? If not how do i make a battery pack for 12v with better performance. The battery i have is Panasonic CGR18650C.

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gandymarsh

1 year ago

It sounds like your batteries must be old. Normally, lithium Ion batteries are 4.2 volts fully charged and shouldn't be discharged below 3 volts.

3 new fully charged batteries in series would put out ~12.6 volts which would probably be enough to run your deck.

You would need to have two or more sets of three in series connected in parallel to increase capacity. Batteries in series have the same capacity and amps as a single battery, the voltage goes up. Batteries in parallel have the same voltage as a single battery, the amps and capacity go up.

Unless you plan to charge the cells individually, which you can do if you use battery holders, there is also the question of charging. Over charging and over discharging can be hard on batteries and dangerous.

There are a lot of things you need to know before building battery packs. You should really learn more about the subject from someone skilled in building them..

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ansaridanishgandymarsh

Reply 1 year ago

No they are 4.2volts as regular 18650 batteries, and yes i took then from a very old laptop battery.
So should i charge them individually to 4.2v to check if they are suitable for the battery pack or not?
Normally i don't plan to charge them individually but as a whole set. I'm also using a bms for the safety of batteries.
But can i charge the cells using the bms while letting the cells give output supply to the speaker??