I was in a similar situation, I bought some Rechargable Lithium-Ion D batteries. 8 of them will cost you about $60, but it's so worth it. On a full charge they last about twice as long as a set of brand new regular non-rechargable D batteries.

https://www.amazon.com/BUMP-1-5V-Rechargeable-Batteries-Requirements/dp/B07TDD3SSF/