Nickel metal rechargeables are a good AA/AAA substitute for devices designed to tolerate their lower voltage. For more power, 14500/18650/21700 cylindrical lithium cells are my go-to.
Personally though, I find it more convenient to have a charging cable on hand vs keep some charged batteries on standby. When the built-in battery eventually goes bad, I am confident that I could replace it myself (not a universal position).