Any android phone from the past 5/6 years, install Lineage, use a USB-C to HDMI Converter that has a charging input (they exist)

I’ve bought some brand called MightyMax on the rainforest site for replacement UPS batteries They work good. My friend who works IT swears by them to recondition old APC Schneider units.

Generally cheap sealed AGM lead acids are a lot safer than cheap lithium, the chemistry is simpler, harder to fuck up and the internal safeties are mechanical, not BMS based. Thry may have slightly lower capacity than a name brand cell but for emergency backup when home labbing it won’t matter.