Extra batteries are good to have. I got these recently:
https://www.amazon.com/DSLRKIT-Parallel-Battery-Convertor-Adapter/dp/B00OUM17AQ/ref=sr_1_5?sr=8-5

I'm finding that I am narrowing down my battery needs to the least number of 'types' and this helps so I can still run D-cell items with the AA cells I've got on hand.