Battery powered raspberry pi

[ohrly?]

This year, we had problems with the unstable power supply for our onboard raspberry pi. I'm a little stuck as to how to solve that:

Option a) get a battery for the raspberry pi -> illegal under R34 because it is not an integral battery. Can I get around this rule, assuming it doesn't change?

Option b) use a laptop -> laptops are usually comparatively heavy and big. Does anyone know a lightweight, cheap laptop with at least 2 USB ports and Ethernet? [a 3rd USB port for an Ethernet dongle is fine]

Option c) somehow guarantee the availability of 1 amp for the raspberry pi?

Option d) can anyone else think of another option?

Thanks so much for any help you can give me!