I have considered that. Do you have any converter in mind? 42V to 36V or less?
Dropping very few volts should raise efficiency. Stepdown modules seem to be more common, more efficient and cheaper than boost step-up modules.
I am using several of these and they work well:
https://www.ebay.com/itm/404206822347DC CC 9A 300W Step Down Buck Converter 5-40V To 1.2-35V Power module
They are nominally limited to 40 V input. It may be that
(1) you could find one with a higher input or
(2) you could measure and find the batteries do not go up that high or,
(3) the device will accept a few more volts for a while without problem.
They are cheap enough that you can test them. I bought a bunch of them and have them around for whenever I need one. I have one right next to me feeding a printer that requires two different voltages and I do not have the original PSU. Rather than providing the two voltages I just supply the higher one and step down from there.