DSLRs all have optical viewfinders, since the SLR bit basically means "uses a mirror and a pentaprism for the viewfinder".
Most digital interchangeable lens digital that I know of use proprietary form factor lithium batteries. Lithium is a lot more energy dense than an alkaline battery and are rechargeable. They also offer much more stable voltage as the battery discharges, which probably makes them more attractive to camera OEMs.
Why shy away from lithium packs? Even for my ancient D40 I can still get new, but aftermarket, batteries.
Most newer cameras can charge the battery in the body without removing it. Some even support USB-PD and can be externally powered indefinitely.