system
Given the following post, respond as if you're commenting on Reddit:
human
[Alien franchise] What kind of power cell/reactor does the David series of androids have? How long can they remain functional if they don't have a method handy to recharge their batteries?
gpt
From the Xenopedia entry on Synthetics

> Power for the android is supplied by a 25 kW hydrogen fuel cell with a life of approximately 400 days between refuelling. This power cell is located within the android's chest, and access is via a hidden socket located just underneath the rib-cage. Charging time can vary, though it usually takes at least 72 hours to fully charge the standard power cells fitted into modern day androids.

Assuming David had access to some basic science tools he could in theory extract some H2 and charge himself up with Hydrogen. 

Possibly using Shaws / Engineers hazard suits? The Engineers must have been advanced enough to have science-y shit laying around and David knew enough about the Engineers to pilot one of their space ships.