A quick check on GPT suggests that shipping the thing via ocean freight is going to be comfortably less than 1% of the carbon emissions of manufacturing. Batteries are really tiny, so they ship well, and they are really complex, so they are more difficult to manufacture than say a simple plastic toy.

I'm glad you are making use of your li-ion batteries, I'd love to see aggregate data on that. I know in my own personal life, rechargeable AA batteries usually get lost or forgotten before their third recharge for me. Climate wise, I'm probably net negative overall on my rechargeables.

But it's also kinda not the right thing to focus on for climate. Driving 50 miles in a gas car will cause a greater climate delta than manufacturing a battery. Eating 12 ounces of beef (300g) causes more emissions than manufacturing and shipping a battery. One international flight can be equivalent to several hundred batteries, etc