Question: Which battle taking place in 7th century England was the result of peace overtures from Augustine's English mission by the Synod of Chester where the armies of the combined Welsh kingdoms of Powys and Rhôs were virtually annihilated?

Context paragraphs:
Llandrindod Wells: Llandrindod Wells (Welsh: "Llandrindod" ,  "Trinity Parish") is a town and community in Powys, within the historic boundaries of Radnorshire, Wales.  It serves as the seat of Powys County Council and thus the administrative centre of Powys.  It was developed as a spa town in the 19th century, with a boom in the late 20th century as a centre of local government.  Before the 1860s the site of the town was common land in Llanfihangel Cefn-llys parish.  Llandrindod Wells is the fifth largest town in Powys, and the largest in Radnorshire.  The Town Council has 15 Members and 1 Clerk.  The Current Mayor is Cllr Jon Williams and The Deputy, Mrs Elaine Worgan.  The Clerk to the Council and The Town is Mrs Jane Johnston - CilCa Wales.

Kingdom of Gwent: Gwent (Old Welsh: "Guent" ) was a medieval Welsh kingdom, lying between the Rivers Wye and Usk.  It existed from the end of Roman rule in Britain in about the 5th century until the Norman conquest of England in the 11th century.  Along with its neighbour Glywyssing, it seems to have had a great deal of cultural continuity with the earlier Silures, keeping their own courts and diocese separate from the rest of Wales until their conquest by Gruffydd ap Llywelyn.  Although it recovered its independence after his death in 1063, Gwent was the first of the Welsh kingdoms to be overrun following the Norman conquest.

Siege of Fort Mose: The Battle of Fort Mose (often called Bloody Mose, or Bloody Moosa at the time) was a significant action of the War of Jenkins’ Ear, and it took place on June 26 of 1740.  Captain Antonio Salgado commanded a Spanish column of 300 regular troops, backed by the free black militia and allied Seminole warriors consisting of Indian auxiliaries.  They stormed Fort Mose, a strategically crucial position newly held by 170 British soldiers under Colonel John Palmer.  This garrison had taken the fort as part of James Oglethorpe's offensive to capture St. Augustine.  Taken by surprise, the British garrison was virtually annihilated.  Colonel Palmer, three captains and three lieutenants were among the British troops killed in action.  The battle destroyed the fort.  The Spanish did not rebuild it until 1752.

Synod of Chester: The Synod of Chester (Medieval Latin: "Sinodus Urbis Legion(um)") was an ecclesiastical council of bishops held in Chester in the late 6th or early 7th century.  The period is known from only a few surviving sources, so dates and accounts vary, but it seems to have been a major event in the history of Wales and England, where the native British bishops rejected overtures of peace from Augustine's English mission.  This led directly to the Battle of Chester, where Æthelfrith of Northumbria seems to have killed the kings of Powys and (possibly) Gwynedd during an attack on the ecclesiastical community at Bangor-on-Dee.

Battle of Mechain: The Battle of Mechain was fought in 1069 in Powys, Wales, for rule of the Welsh kingdoms of Gwynedd and Powys.

Battle of Chester: The Battle of Chester (Old Welsh: "Guaith Caer Legion"; Welsh: "Brwydr Caer") was a major victory for the Anglo Saxons over the native Britons near the city of Chester, England in the early 7th century.  Æthelfrith of Northumbria annihilated a combined force from the Welsh kingdoms of Powys, Rhôs (a cantref of the Kingdom of Gwynedd) and possibly Mercia.  It resulted in the deaths of Welsh leaders Selyf Sarffgadau of Powys and Cadwal Crysban of Rhôs.  Circumstantial evidence suggests that King Iago of Gwynedd may have also been killed.

Kanalkampf: The Kanalkampf (Channel Battle) was the German name for air operations by the German "Luftwaffe" against the British Royal Air Force (RAF) over the English Channel, which marked the beginning of the Battle of Britain in July 1940, during the Second World War.  By 25 June, the Allies had been defeated in Western Europe and Scandinavia.  Britain rejected peace overtures and on 16 July, Adolf Hitler issued Directive 16 to the "Wehrmacht" (German armed forces), ordering preparations for the invasion of Britain, under the codename "Unternehmen Seelöwe" (Operation Sea Lion).

Battle of Hereford: The Battle of Hereford was fought in 760 at Hereford (in what is now Herefordshire, England).  The conflict followed decades of hostility between the Welsh Kingdoms of Brycheiniog, Gwent and Powys by Æthelbald of Mercia and Coenred of Wessex, and involved the armies of Mercia and the Welsh.  The Welsh were said to have defeated the Mercian army, and freed themselves from the influence of the Anglo-Saxons.

Battle of Ruxu (222–223): The Battle of Ruxu, also known as the Battle of Ruxukou, took place in 222-223 between the forces of Cao Wei and Eastern Wu during the Three Kingdoms period.  The battle was the third battle taking place between the Cao and Sun clan at Ruxu, but this particular conflict was the only of the three to take place actually during the Three Kingdoms period, as the other two took place in 213 and 217.

Rhwng Gwy a Hafren: Rhwng Gwy a Hafren (English: "Between Wye and Severn" ) was a region of medieval Wales, located in the Welsh Marches between Powys to the north and Brycheiniog to the south.  It was bounded by the rivers Wye (Welsh: "Gwy" ) and Severn (Welsh: "Hafren" ).  It covered about the same territory as Radnorshire, now part of the county of Powys.  The region first came into its own in the 9th or 10th centuries, when it was ruled by leaders who operated independently of the surrounding kingdoms.  After the Norman invasion, it comprised the central part of the Welsh Marches and was the site of frequent struggles between Welsh and Norman forces.

Supporting paragraphs: Synod of Chester Battle of Chester
Answer: Battle of Chester