Nice compromise would be LFP cells. 3.2V, charges from a LK-100B, but you have to remember to always press Da Button when starting it up. Otherwise it’ll assume it’s a Li-ion cell and try charging it to 4.2V vs 3.6V. That would be a Bad Thing. But at least you’re playing with 3.2V pretty much flat over its whole discharge curve, vs 1.2V.