Solar shower bag or battery-powered pump — which is better for camping?

They solve different problems. Solar bags (like the Advanced Elements Summer Shower) are cheap, silent, and heat water passively in the sun, but they're awkward to hang full and water pressure tails off as the bag empties. Battery-powered pumps (Ivation, Spopal) draw from any bucket or jug and deliver consistent pressure, but they don't heat water and you'll need to warm it yourself. Overlanders running longer trips often choose pressurized or propane systems despite the higher price and bulk.