Lithium Polymer 3.7V 2520mAh 9.32Wh U46P313

Here are Genuine U46P313 Rechargable Lithium Polymer Batteries!  Inside each battery is a 3.7v 2520mAh 9.32Wh cell and a 3a BMS. You can charge and discharge through the positive and negative terminals so these are like batteries with a PCB protection circuit which makes assembling a battery very safe. Most customers are simply trimming some of the plastic off and soldering lead wires directly to the + and - connectors. Some are using a folded piece of nickel to slide in like a blade. You can expect around 90% capacity as these were only cycled a few times.

At 80 cents per battery that comes out to just $85/kWh for batteries with a BMS that works like a smart cell level fusing. Simply charge each pack up to 4.2v, make your series and parallel connections, then add an overall pack BMS and you are ready to go with a very safe and long lasting battery pack. Perfect for many applications with 1c discharge abilities and 0.5c charge abilities. Those specs are good for most applications and especially great for powerwalls.

Photos 4-8 show a great connection idea for 20 cell bricks. That brick would be 3.7v, 50.4ah 186.48wh and just 5.25" x 2.25"x 2.25". Capable of 50a discharge and 25a charge rate. Run a busbar up the sides and use standard nickel like a blade connector. Just fold the one end of the nickel to make a stronger connection into the cell. When one cell goes bad down the road the BMS cuts off and the rest of the pack continues working like normal minus that one cell.