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Success with first electric go kart project (pics)
Excellent information.  I am learning more each day and I appreciate the advice.  I am using new LG MJ1 3500 mAh 18650 battery cells connected with pure nickel strips.  I used a spot welder for the nickel strips and 40/60 Rosin/Lead solder for the wire connections.  I will purchase the lower capacity/higher discard batteries as recommended.  I know this is a very small project but it is fascinating to know that I am driving a go kart using electrons instead of gas power.  
Asy you are keen on learning stuff, here is some more for you to digest Smile

When getting new cells you should always take the time to check the datasheet. It will always tell you something useful.
In case of the MJ1, the max discharge is 10A so you are running your cells right at the limit, probably even a bit beyond. And while you can do it this doesn't mean you should do it. It impacts the life expectancy of the cell and also the performance, as you have seen.
Since you've already started with the MJ1, stick with the MJ1, but double the amount of cells and go for 7s4p. Or even bigger, as much as the available space allows. You will also see that doubling the cells will give your actually more than double the runtime because the useable capacity increases with lower load. Also, the max energy per cell will increase because the average voltage will be higher with lower load.

Also, LG specifies resting time for the cells after charging (10 minutes) and after a high load discharge (20 minutes). So don't charge the cells right after using them and don't use them in the kart right after charging them
Thanks DarkRaven. I will  increase the battery pack size to 4P or maybe 5P in the near future. It should not be too difficult since I have a spot welder and can just add more cells to the current configuration (see pic). I will also order some Samsung INR18650-25R 2500 mAh 18650 battery cells for future projects. They can discharge at 20A and have a C Rate of ove 8.0. Thanks for the advice.

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Samsungs INR18650-25 cells are very popular for power tools and such. Very good and reliable cell, good choice!
So I just added more capacity to the battery. I now have a 7S4P configuration (and as everyone predicted) the resulting power increase was noticeable. I can easily make it up my driveway and I managed my first official “drift” on a nearby vacant road.  The experience has been great and I am enjoying the learning process. I will soon upgrade to a 48v motor/charge controller and a new battery pack (probably 14S/8P) using the higher discharge Samsung 18650 cells.  I really appreciate everyone’s feedback and I look forward to posting results of the upgrade.
That contraption looks like fun. 48v motor should really spice things up for you. Smile
So before I upgrade to the 48 volt motor/controller, I increased the size of the existing battery pack to 7S7P.  The increase in power was very noticeable and I learned a few more things. I added a small volt meter so I can ensure I do not drop below a certain power level. Thanks again fo all of the advice so far. I will post pictures of the upcoming 48 volt motor installation.

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You can't do that endlessly though, at some point more cells in parallel won't give you more power and just increase the runtime Smile
By the way, you were a bit generous on the main positive connection (and I guess on the main negative one as well). You can do it like that and go all the way down the length of the battery, but you don't need to. It has no beneficial effect. The cells are already connected, you are just providing a bigger connection between the terminals of the cells and it doesn't effect the way current flows through the main wire.
Thanks DarkRaven. I thought I had to run the wire down the length of the positive and negative terminal parallel cells but I guess I was wrong. I appreciate the information since I am learning as I go. This is a fun project
So I gave into the temptation for more power. Smile   I will soon replace the components on the electric go cart referenced above with the following set up: 
  • 48V 1000 Watt Brushed Motor with rated current of 26.7 amps

  • 48V charge controller

  • 14S9P batteries using Samsung INR18650-25R 2500 mAh 18650 cells (connected with spot welder using pure nickel strips)

I added a 35 amp fuse (rated for up to 58 volts) and I hope to hook everything up to the go kart this weekend. Thanks to those on this forum who have provided advice to me. I really appreciate it. Here are a few photos of the new battery pack I created and the motor/charge controller that I will soon install.
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