(covers information from an alternate timeline)
"Well, we can't just run up a white flag."
The Battle of Ceti Alpha V was a battle between the remnants of Humanity and the Xindi in 2165 of an alternate timeline. This timeline represented the worst-case outcome of the Xindi crisis for Humanity, and would have likely led to the Sphere-Builders successfully conquering the Milky Way Galaxy within a few centuries. (ENT: "Twilight", "Azati Prime")
In 2153, while searching for the Xindi weapon in the Delphic Expanse, Captain Jonathan Archer was infected with interspatial parasites while trying to save T'Pol from a spatial anomaly. As a result of amnesia which the parasites induced, Archer was rendered incapable of commanding Enterprise NX-01 and T'Pol accepted a Starfleet commission to become captain. However, when fighting two Xindi-Reptilian warships sometime later, Enterprise sustained critical damage to its starboard warp nacelle, which prevented the ship from exceeding warp 1.7. Unable to traverse the Expanse at an acceptable speed, the crew failed to prevent the Xindi from launching their weapon and destroying Earth in 2154. The Xindi then proceeded to wipe out every Human settlement they could find – Mars, Alpha Centauri and Vega colony quickly fell, their entire populations slaughtered.
The remnants of Humanity, around 6,000 people, eventually settled on Ceti Alpha V in 2156, while the Xindi hunted the galaxy for them. The Vulcan High Command and Andorian Empire offered limited support, respectively providing supplies and deflector shield technology. T'Pol eventually resigned from Starfleet to take care of Archer, leaving Charles Tucker III to take command.
Determined to cure Archer, Doctor Phlox spent the next twelve years searching for a way. After learning that the only existing way to destroy the parasites would be to vaporize Archer in a subspace implosion, Phlox worked on developing his own treatment and came up with an antiproton beam powered by Enterprise's warp core. The first use of the beam eliminated one of three clusters of the parasites in Archer's head. Phlox and T'Pol noticed that the parasites had also disappeared in all of the previous scans taken by Phlox, suggesting that the parasites existed outside of time, and realized that if they completed the treatment, they would be eliminated in the past too. This outcome could potentially alter the timeline for the better, as Archer would never have been infected and could conceivably lead the Enterprise to victory over the Xindi.
Before the treatments could resume, Enterprise captured a Yridian spy who had informed the Xindi of the location of the remnants of Humanity. Needing all power for the weapons, Captain Tucker ended the treatments and, shortly afterwards, six Xindi ships – three Insectoid, three Reptilian – were detected entering the system and heading for Ceti Alpha V. (ENT: "Twilight")
Enterprise engaged the six Xindi ships with phase cannons. Though the ships returned fire, the new shields held. Enterprise broke off and was followed by an Insectoid vessel and a Reptilian ship while the rest headed for the planet. As the two ships chased the Enterprise around an asteroid, they were attacked from behind by the Intrepid and another starship, disabling the Insectoid ship. The Enterprise then turned around and fired on the Reptilian ship, knocking out its engines. The defeat of their two ships caused the four remaining Xindi craft to alter course to engage the three defenders.
Under heavy attack, Enterprise managed to destroy an Insectoid ship, but started taking damage itself, with forward shielding going down to fifty-two percent. An Insectoid ship and a Reptilian vessel targeted the Intrepid together, blasting off its port nacelle. With no other choice, Tucker ordered them to retreat. Enterprise then lost phase cannons to a hit. The forward shield collapsed, and Enterprise suffered hull breaches on B and C decks. With the forward shields down, the Xindi ships targeted the bridge and blasted the top off of it, killing Tucker and his entire bridge crew.
As Reptilian boarding parties beamed aboard the Enterprise, T'Pol ordered Phlox to meet her and Archer in engineering to complete his treatment, hoping that doing so would reset the timeline. In engineering, Phlox discovered that the chamber used in the treatment had been destroyed by debris and was unusable. Archer remembered Phlox telling him that the parasites could also be destroyed by a subspace implosion which would destroy the Enterprise as well, but with the battle clearly lost, they saw no other choice. Archer ordered T'Pol and Phlox to leave in a shuttlepod, reasoning that, if he failed to reset history, the Xindi might ignore them as they were only targeting Humans. Both refused, and the trio set to work overloading three plasma injectors.
Discovering that one of the injectors had been damaged, Archer sent Phlox to get a replacement from a supply locker which he used to successfully replace the damaged injector. Overcoming nearby security teams, Xindi boarding parties entered engineering and killed Phlox. T'Pol overloaded the first injector, as Archer laid down covering fire, but was killed before she could finish. Archer took over, overloading the second injector as he exchanged fire with the Xindi, taking several hits. Mortally wounded, Archer managed to overload the final injector, moments before dying. The ensuing subspace implosion consumed the Enterprise, destroying the ship, its remaining crew, the boarding parties, and the parasites. (ENT: "Twilight")
As hoped, the subspace implosion destroyed the parasites in all time periods, resulting in Archer only suffering a concussion and no amnesia from the incident in 2153. Without the amnesia, Archer was able to remain in command of Enterprise NX-01, resulting in a different outcome to the Xindi incident, in which the weapon was destroyed before it could reach Earth. (ENT: "Twilight", "Zero Hour")
Had the alternate timeline not been nullified, the Xindi presumably would have won the battle and destroyed Ceti Alpha V. Without Humanity, the United Federation of Planets would never have been founded, ultimately dooming the galaxy when the Sphere-Builders invaded, centuries later. (ENT: "Azati Prime")