this is a big battery power bank to make a difference

Step 1: Why U Need to Make It

the power banks in the market aren't enough to charge your tablet and smartphone simultaneously multiple times
batteries are lying around in ur house
u want to learn something new by building your own power bank

Step 2: About the Batteries THEY ARE LIKE LEGO BRICKS

these are 18650 batteries different from regular AA batteries in size and capacity
one 18650battery is equal to 9 AA batteries in power
even they are rechargeable
they have the highest power to weight ratio
and even last around 4-5 years or 300 cycles
tesla motors used these type of cells in Thier cars and other projects

i got them from my old powerbank,old laptop batteries and from the junkyard for FREEEEEE

Step 3: What You Need

1.batteries-18650
2.cardboard box
3.powerbank circuit
4.tools

Step 4: Gather All the Stuff

Step 5: Lets Start With the Box

cut out the cardboard and tape it up in the shape of a box
make sure that you have a good quality of cardboard bcoz this will only determine the build quality of our powerbank

Step 6: Tape Up the Batteries

make a rugged and durable tape joint all through

Step 7: Battery Testing Time

make sure that none of the battery is dead
max charge voltage 4.2v
min idle voltage 3.6v
during use min voltage 3.2v
try to recover the dead batteries by giving them a jolt of electricity
if they regain their capacity then we can use them if not then they are of no use here

Step 8: CONNECT THEM IN PARALLEL

i used soldering to connect them that may not be the best way of connecting
but there are several ways that are more healthy for the batteries but difficult for me to do