This video shows how I assembled a 12V LiFePO4 (lithium iron phosphate) battery to upgrade our older Solo 416 backpack sprayer. Sorry for the rambling and excessive length. Someday maybe I'll learn to script this stuff, or edit it properly.

The new pack is 4S3P configuration using 26650 cells rated each at 3.8Ah. The completed pack tested at 11.5Ah (145Wh) on a load tester simulating the application load of 3.5A, providing more than 3hrs of runtime.

The video also briefly covers the use of a Meanwell DC power supply as CC/CV charger.

Parts used in this build include:
K2 LiFePO4 cells in 26650 format
https://batteryhookup.com/products/16...

40A 4S LiFePO4 BMS with balance
https://www.aliexpress.com/item/33037...

Amass XT-60 connectors
https://www.aliexpress.com/item/40002...
https://www.aliexpress.com/item/10050...

Meanwell RSP-75-13.5 power supply with CC-CV overload
https://www.mouser.ca/ProductDetail/M...