I’ve used a BLF-1206 with KX3 and also an FT-100 at various power levels on summits.
Also used a BLF-1215 with a TS-480SAT @ 100W for almost 7 hours with mix of CW and SSB during a past NA/EU S2S day.
Also chased from home with KX3 + BLF-1206 for 2 days (daytime ops) and still had reserve charge. Or 23+ hours just Rx.
I prefer batteries with a BMG like these have. BLF also includes an integral balance charge circuit.
I’m just a customer but happy with their products and service.