Need help diy a power bank

[mikey5791]

Hi friends,

Got this simple power bank of 8800mAh capacity but the inside battery seems to be failing. It is not taking any more useful charge. The dmm measured the battery reading about 0.17vdc. The input is rated at 5v 2.0A. I was thinking about replacing the failed battery with some extra batteries from my used laptop battery pack.

The laptop battery pack is AL15A32( rating 14.8v 2350mAh) consisted of 4 series joined 18650 type li ion battery. However, one of the battery showed only 0.15vdc but the remaining 3 are still within 3.77v to 4.21vdc. Is it possible and safe to cut off the 3 li ion battery and solder to the power bank connector and try charging with an off the shelf 5v 1.5A phone charger? I wish to rebuild this set of battery pack as a power bank and hope for any advice if this can be done.

[stj]

Re: Need help diy a power bank

you have 2 questions there.

lets deal with the laptop pack first.
get rid of the small board from the battery pack,
solder wires to the tabs of the almost dead battery.
then connect those wires to a 5v supply - like a usb psu, BUT put a 75ohm resistor in series with it.
that will very slowly charge the battery back up over a day or 2

[sam_sam_sam]

Re: Need help diy a power bank

The dmm measured the battery reading about 0.17vdc.

However, one of the battery showed only 0.15vdc

These two are no good remove and do not use them or even attempt to try to charge them—> Doing this could be very dangerous undertaking when the voltage is this low more than likely are shorting internally and would charge anyway

I personally would not attempt to charge any li ion battery that is lower than 1.0 volts however you could try to charge batteries over one volt using the method below as well but to do this use a lot of caution watching the temperature of the battery unit the battery voltage come up to 2 volts

Now STJ has in his post to charge a battery that is above 2 to 3 volts I would totally recommend and would agree with ( on a side note I would use the battery bank pack board with current limiting resistor like STJ had in his post earlier)

Now you can use 18650 in this battery bank pack but I am going to caution you about pouch type li ion batteries unsolder the tabs from the board or cut the tabs do not be temped to rip it from the board this will probably damage the board and the battery if you were to want to reuse the battery or charging board if they are still good

Now if you decide to use the 18650 battery cells from the computer battery pack cut the tabbing from the protection board and to separate the cells from each other you can pull them apart or cut them in the middle of each cell so you have soldering tab to join the battery cells together

But you would need to find a case that will fit the battery or batteries and charger board and yes you can use more than one cells wired in parallel but I will caution you that if you are going to rely on the fuel gauge on the battery pack limit the number of cells to the maximum battery amp hours that posted on the data plate on the case of your battery bank pack

When you hook the battery to the battery charging board you might notice that you have no battery power from the board this is normal on some board just hook it to your charger and this will reset the protection circuit on the board and it should function after you do this

I hope this help

[mikey5791]

Re: Need help diy a power bank

Hi stj and sam x3,

Before i start this project, i will try to find a bigger case for the new battery pack.
I will look into all the suggested comments.

Thank you for reply.