diff --git a/chat_archiver/chat_archiver/main.py b/chat_archiver/chat_archiver/main.py
index d112894..a40f81c 100644
--- a/chat_archiver/chat_archiver/main.py
+++ b/chat_archiver/chat_archiver/main.py
@@ -1,4 +1,5 @@
 
+from calendar import timegm
 import base64
 import hashlib
 import json
@@ -178,12 +179,16 @@ def write_batch(path, batch_time, messages):
 	time = datetime.utcfromtimestamp(batch_time).strftime("%Y-%m-%dT%H:%M:%S")
 	filename = "{}-{}.json".format(time, hash)
 	filepath = os.path.join(path, filename)
-	temppath = "{}.{}.temp".format(filepath, uuid4())
-	ensure_directory(filepath)
-	with open(temppath, 'wb') as f:
-		f.write(output)
-	os.rename(temppath, filepath)
-	logging.info("Wrote batch {}".format(filepath))
+	if os.path.exists(filepath):
+		logging.info("Not writing batch {} - already exists.".format(filename))
+	else:
+		temppath = "{}.{}.temp".format(filepath, uuid4())
+		ensure_directory(filepath)
+		with open(temppath, 'wb') as f:
+			f.write(output)
+		os.rename(temppath, filepath)
+		logging.info("Wrote batch {}".format(filepath))
+	return filepath
 
 
 def format_batch(messages):
@@ -210,6 +215,25 @@ def get_batch_files(path, batch_time):
 	]
 
 
+def merge_all(path):
+	"""Repeatedly scans the batch directory for batch files with the same batch time, and merges them.
+	Returns once it finds no duplicate files."""
+	while True:
+		by_time = {}
+		for name in os.listdir(path):
+			if not name.endswith(".json"):
+				continue
+			timestamp = "-".join(name.split("-")[:3])
+			by_time[timestamp] = by_time.get(timestamp, 0) + 1
+		if not any(count > 1 for timestamp, count in by_time.items()):
+			break
+		for timestamp, count in by_time.items():
+			if count > 1:
+				logging.info("Merging {} batches at time {}".format(count, timestamp))
+				batch_time = timegm(time.strptime(timestamp, "%Y-%m-%dT%H:%M:%S"))
+				merge_batch_files(path, batch_time)
+
+
 def merge_batch_files(path, batch_time):
 	"""For the given batch time, merges all the following messages:
 	- From batch files at that time
@@ -241,15 +265,19 @@ def merge_batch_files(path, batch_time):
 		batch = [json.loads(line) for line in batch.strip().split("\n")]
 		messages = merge_messages(messages, batch)
 
-	# sorting by time is needed for group_by(), we'll sort properly on save.
-	messages.sort(key=lambda message: message['time'])
-	for batch_time, batch in itertools.group_by(messages, key=
-		lambda message: int(message['time'] / BATCH_INTERVAL) * BATCH_INTERVAL
-	):
-		write_batch(path, batch_time, batch)
+	by_time = {}
+	for message in messages:
+		batch_time = int(message['time'] / BATCH_INTERVAL) * BATCH_INTERVAL
+		by_time.setdefault(batch_time, []).append(message)
+
+	written = []
+	for batch_time, batch in by_time.items():
+		written.append(write_batch(path, batch_time, batch))
 
 	for batch_file in batch_files:
-		os.remove(batch_file)
+		# don't delete something we just (re-)wrote
+		if batch_file not in written:
+			os.remove(batch_file)
 
 def merge_messages(left, right):
 	"""Merges two lists of messages into one merged list.
@@ -289,7 +317,7 @@ def merge_messages(left, right):
 			# by the same recipient.
 			for k in receivers.keys():
 				for old in (a, b):
-					if k in old and old[k] != recievers[k]:
+					if k in old and old[k] != receivers[k]:
 						raise ValueError(f"Merge would merge two messages with different recipient timestamps: {a}, {b}")
 			return a | {
 				"time": o[0],
@@ -303,7 +331,7 @@ def merge_messages(left, right):
 	unmatched = [], []
 	for messages, u in zip((left, right), unmatched):
 		for message in messages:
-			id = message.get('tags', {}).get('id')
+			id = (message.get('tags') or {}).get('id')
 			if id:
 				by_id.setdefault(id, []).append(message)
 			else:
diff --git a/chat_archiver/chat_archiver/merge_all.py b/chat_archiver/chat_archiver/merge_all.py
new file mode 100644
index 0000000..a9f0e65
--- /dev/null
+++ b/chat_archiver/chat_archiver/merge_all.py
@@ -0,0 +1,14 @@
+
+import argh
+import logging
+import json
+
+from .main import merge_messages, format_batch, merge_all
+
+def main(path, log='INFO'):
+	"""Merge all batch files with the same timestamp within given directory"""
+	logging.basicConfig(level=log)
+	merge_all(path)
+
+if __name__ == '__main__':
+	argh.dispatch_command(main)