I got a bunch of 74Ah high-output Japanese surplus LiFePO4 cells (note the high output chemistry is rated for 2.0V to 3.5V range, not the typical 2.5V to 3.65V for other LiFePO4 cells). These small 74Ah cells can output 180 Amperes continuously and 600 Amperes for 20 seconds. Great for powering high-output inverters with small backup capacity in a small place and small cost. 

AliExpress has FR4 spacers for the 280Ah-320Ah size cells, and they cost a bit and take a while to arrive. I made these so they neatly connect in a grid. See drawings. The 16S2P array could power up to a 14kW inverter.

I printed these in PETG for extra temperature range, in 2 layers at 0.28mm per layer, including first layer.

The concept is easily extended to other array sizes and batteries.