Bioenno Power has been supplying best-in-class LiFePO4 batteries for the amateur radio operator for over a decade now. Unlike some of the garbage sold on Amazon, their stuff meets specs and lasts for many years.
They have monthly-ish Buy One, Get One Free sales. The current sale is for their 12 volt 3 AH battery. This is a perfect size for QRP fans and will support hours of field activations in a very tiny package.
Maybe buy a pair with chargers and split the cost with a friend?