Stepping down battery voltage/size

So I have a decent amount of experiance building boards now and have a decent collection of parts and I have an old battery (15s2p) and a esc capable of 10s. I was wondering if anyone has any ideas for making these parts work that doesnt require rebuilding the battery.

I was thinking about using something like a buck converter like this (this one specificly obviously wont work) 63v dc converter - Buy 63v dc converter with free shipping on AliExpress

Buck has limits. It will not hold up to that kind of use.