I was talking about the first 3rd of the battery. In the case of barely getting to 70% that was a case where the lantern was running at like 1/4rd power also.
I would suggest two strings of 4 LEDs. One for each color temp. That way the current is the same in each LED and binning variances can’t lead to one pulling more current than the others. A 2S2P battery configuration would be better than 1S4P, but that complicates the battery situation by using unprotected batteries in series which is ill advised.
Why does everyone want to toss an additional 20-30% of the battery life at lower brightness levels (not that much on high)? The reasons you cite for efficiency not being a big concern actually are reasons why the efficiency is even worse in this lantern than lights pulling more current with fewer batteries. The low LED current means lower forward voltages. This means more power is burned off in the driver. The four batteries in parallel mean the per cell current draw is quite low meaning the cell voltage sags less and stays at a high voltage longer meaning more power is burned up in the driver.
Boost drivers aren’t hard. I don’t understand why everyone is scared of them or doesn’t want to use them.