Have it just be form-fitted outside contacts, with magnetic adhesion to hold the plug in place.
I actually really like this idea. If we’re breaking backwards compatibility anyways, let’s do something useful with it. This form factor was invented in the 1950s. I’m sure we can do something better now.
We need to move away from everything having a battery anyways. Wireless headphones were a mistake. Now people are walking around with 4-6 batteries on them at all times. Phone, laptop, earbuds, earbud case, battery backup, smart watch. Batteries aren’t great for the environment, not to mention they typically condemn something to being tech waste in a few short years. We need to significantly rethink this model.