The Precursor Sentry is a boss from Jak and Daxter: The Precursor Legacy VII. It is fought at The Waterworks. This metal-headed guard robot attacks anyone who activates it. Unfortunately, it is the only thing capable of destroying the Lurker dam preventing the river from flowing south. To start the battle, get a Blue Eco charge and walk up to it. This will breathe life into the machine, but you'll now have to undo this action.
The Precursor Sentry attacks by slamming its two comically large iron fists like hammers on the ground. It hovers around at a fairly slow pace, but you won't be able to run away from the battle. It also fires blue lasers from its eyes, but these are not too difficult to avoid with some good rolling and springing techniques. Its most annoying attack involves sending a frenzy of metal pieces off of its body spinning all around- try to not get nailed with any shrapnel. After it does this attack, it exposes the central crystal of its body, but only until it reattaches its lost pieces. During this time, get some Yellow Eco and fire it at the crystal to damage the sentry. This must be done a few times to defeat the boss, but it will gradually become faster in addition to using a spinning attack and a powerful explosive red beam attack which should be avoided at all costs. After its defeat, the resulting explosion will destroy the whole dam, and you'll get the boss' Power Cell.