I know that having batteries at the ready for Coders can sometimes be a tricky situation, and are often something you might not have on hand in your classroom. Rechargeable batteries offer a potential solution - but only if they don’t need to be charged often.
I recently learned about these Rechargeable Lithium AAA batteries (Amazon link) that are compatible with the VEX Coder and charge with a USB-C! A box of 12 would service 6 Coders (so a whole bundle set) and the whole set will charge with the same charger as the 123 Robot itself.
Some testing with Coders and robots showed that these batteries supported a HUGE number of projects to be run on a single battery charge. I also love that it’s small, compact, and could easily be stored within a bundle bag.
Hope this is helpful for anyone looking to solve their battery woes during the school year 
