Battery and charger suggestion please

I want to mod my TurboExpress to use lipo rather than AAs but I am not quite finding what I want. For the available space, I can have 2 of https://www.sparkfun.com/products/13855 stacked together but I can’t find the charger that can handle both from a single USB source for charging (balance charger I think?) and can output either 5v or 7.4v

Or does Sparkfun carry a larger battery that is roughly 80mmx50mmx14mm maximum?

Thanks for reaching out to us on this.

We sell a balance charger [https://www.sparkfun.com/products/16793*(https://www.sparkfun.com/products/16793[i)] for charging the batteries* ; rigging them up to be discharging in parallel is what it sounds like you are attempting…look up videos on how to wire things in parallel, and then wire the 2 stacked batteries to a single JST connector.

We do not currently carry a better-suited battery for what you’ve described.

Hope this helps, and happy sparking!