Lithium AA batteries offer an impressive operating life. I often use Energizer batteries: they are expensive, but extremely reliable. For rechargeable batteries, I use IKEA LADDA 2450 mAh cells.
My battery charger is a MAHA MH-C800S, which can charge eight batteries simultaneously and has proven to be very dependable. I also carry a 20,000 mAh ESSENCE power bank for my phone.
To power the Sound Devices MixPre-10 II, I rely on AUDIOROOT equipment. I use two eSMART Li-96neo batteries together with the eSMART Dual Charger.