diff --git a/.changeset/quiet-jobs-retry.md b/.changeset/quiet-jobs-retry.md
new file mode 100644
index 00000000..dea4fdda
--- /dev/null
+++ b/.changeset/quiet-jobs-retry.md
@@ -0,0 +1,13 @@
+---
+"graphile-worker": patch
+---
+
+Fix batched `completeJobs`/`failJobs` never being retried. The retry loop in
+`batch()` bailed out of its `catch` with `break`, so `BATCH_RETRY_OPTIONS` was
+dead code: a single transient database error (e.g. a `40P01` deadlock,
+serialization failure or dropped connection) tore the worker pool down instead
+of retrying, leaving the batched jobs locked so they were later re-executed
+(duplicate execution). The failed attempt now falls through to the next
+iteration and is retried with backoff, only throwing once `maxAttempts` is
+exhausted. Also clear the `backpressure` deferred once resolved so the pending
+refcount stays balanced across repeated hold/release cycles.
diff --git a/__tests__/batchRetry.test.ts b/__tests__/batchRetry.test.ts
new file mode 100644
index 00000000..9b0dd938
--- /dev/null
+++ b/__tests__/batchRetry.test.ts
@@ -0,0 +1,157 @@
+import { run } from "../src/index.ts";
+import {
+  ESCAPED_GRAPHILE_WORKER_SCHEMA,
+  reset,
+  sleep,
+  withOptions,
+} from "./helpers.ts";
+
+/**
+ * Regression test for https://github.com/graphile/worker/issues/636
+ *
+ * `batch()` wraps batched completions/failures in a retry loop governed by
+ * `BATCH_RETRY_OPTIONS` (20 attempts, with shorter delays for retryable codes
+ * such as `40P01` deadlock_detected). Previously the loop's `catch` ended with
+ * `break`, so it bailed out after the very first failure and threw - none of
+ * the retry code ran. A single transient error (deadlock / serialization
+ * failure / dropped connection) therefore tore the worker pool down and left
+ * the batched jobs locked, so they were re-executed later (duplicate
+ * execution).
+ *
+ * Here we make the first batched completion fail with `40P01` and let later
+ * attempts succeed; the job should be completed by a retry and the runner
+ * should keep running.
+ */
+test("a batched completion that hits a transient deadlock is retried", () =>
+  withOptions(async (options) => {
+    const { pgPool } = options;
+    await reset(pgPool, options);
+
+    // Fail the *first* DELETE from `_private_jobs` (the batched completion) with
+    // a deadlock_detected (`40P01`) error; every later attempt succeeds.
+    await pgPool.query(`
+      create sequence public.completion_attempts;
+      create or replace function public.deadlock_once() returns trigger
+      language plpgsql as $$
+      begin
+        if nextval('public.completion_attempts') = 1 then
+          raise exception 'simulated deadlock' using errcode = '40P01';
+        end if;
+        return old;
+      end;
+      $$;
+      create trigger deadlock_once
+        before delete on ${ESCAPED_GRAPHILE_WORKER_SCHEMA}._private_jobs
+        for each row execute function public.deadlock_once();
+    `);
+
+    const runner = await run({
+      ...options,
+      taskList: { job1: async () => {} },
+      preset: { worker: { completeJobBatchDelay: 0 } },
+    });
+    let settled = false;
+    runner.promise.then(
+      () => (settled = true),
+      () => (settled = true),
+    );
+    try {
+      await runner.addJob("job1", { id: "1" });
+      let remaining = 1;
+      for (let i = 0; i < 50 && remaining > 0; i++) {
+        await sleep(100);
+        remaining = (
+          await pgPool.query(
+            `select count(*)::int as n from ${ESCAPED_GRAPHILE_WORKER_SCHEMA}._private_jobs`,
+          )
+        ).rows[0].n;
+      }
+      // The completion was retried after the deadlock, so the job is gone and
+      // the runner is still alive (it did NOT tear the pool down).
+      expect({ remaining, runnerStopped: settled }).toEqual({
+        remaining: 0,
+        runnerStopped: false,
+      });
+      // Guard against the test silently becoming a no-op: assert the trigger
+      // actually fired more than once, i.e. the completion was re-attempted
+      // after the simulated deadlock. Without the retry fix this would be 1
+      // (single attempt) and the job would still be present above.
+      const attempts = (
+        await pgPool.query(
+          `select last_value::int as n from public.completion_attempts`,
+        )
+      ).rows[0].n;
+      expect(attempts).toBeGreaterThanOrEqual(2);
+    } finally {
+      await runner.stop().catch(() => {});
+    }
+  }));
+
+/**
+ * The retry loop must only retry *transient* errors. A non-retryable error
+ * (here a plain `raise exception`, SQLSTATE P0001, which is not in
+ * `RETRYABLE_ERROR_CODES`) can never succeed, so `batch()` must fail fast -
+ * one attempt, then throw - rather than looping `BATCH_RETRY_OPTIONS.maxAttempts`
+ * (20) times with backoff, which would delay the fatal shutdown by minutes.
+ */
+test("a batched completion that hits a non-retryable error fails fast (no retry)", () =>
+  withOptions(async (options) => {
+    const { pgPool } = options;
+    await reset(pgPool, options);
+
+    // Every DELETE from `_private_jobs` (the batched completion) raises a
+    // non-retryable error, and each attempt is counted.
+    await pgPool.query(`
+      create sequence public.nonretryable_attempts;
+      create or replace function public.fail_permanently() returns trigger
+      language plpgsql as $$
+      begin
+        perform nextval('public.nonretryable_attempts');
+        raise exception 'permanent failure';
+        return old;
+      end;
+      $$;
+      create trigger fail_permanently
+        before delete on ${ESCAPED_GRAPHILE_WORKER_SCHEMA}._private_jobs
+        for each row execute function public.fail_permanently();
+    `);
+
+    const runner = await run({
+      ...options,
+      taskList: { job1: async () => {} },
+      preset: { worker: { completeJobBatchDelay: 0 } },
+    });
+    let settled = false;
+    runner.promise.then(
+      () => (settled = true),
+      () => (settled = true),
+    );
+    try {
+      await runner.addJob("job1", { id: "1" });
+      // The completion can never succeed, so the runner should tear down
+      // quickly (fail fast), not after 20 backoff attempts.
+      for (let i = 0; i < 50 && !settled; i++) {
+        await sleep(100);
+      }
+      const attempts = (
+        await pgPool.query(
+          `select last_value::int as n, is_called from public.nonretryable_attempts`,
+        )
+      ).rows[0];
+      const remaining = (
+        await pgPool.query(
+          `select count(*)::int as n from ${ESCAPED_GRAPHILE_WORKER_SCHEMA}._private_jobs`,
+        )
+      ).rows[0].n;
+      // Failed fast: the runner stopped, the job is still present (completion
+      // never succeeded), and the completion was attempted exactly once - the
+      // non-retryable error was NOT retried.
+      expect({
+        runnerStopped: settled,
+        remaining,
+        attempts: attempts.is_called ? attempts.n : 0,
+      }).toEqual({ runnerStopped: true, remaining: 1, attempts: 1 });
+    } finally {
+      await runner.stop().catch(() => {});
+    }
+  }));
diff --git a/src/main.ts b/src/main.ts
index 60b06787..0f0a2923 100644
--- a/src/main.ts
+++ b/src/main.ts
@@ -1501,6 +1501,10 @@ function batch<TSpec, TResult>(
   function allgood() {
     if (backpressure) {
       backpressure.resolve();
+      // Clear it so a subsequent `holdup()` creates a fresh deferred (and a
+      // matching `incrementPending()`); otherwise the stale resolved deferred
+      // would suppress future backpressure and unbalance the pending refcount.
+      backpressure = null;
       // Bump a tick to give the things held up by backpressure a chance to register.
       process.nextTick(decrementPending);
     }
@@ -1540,7 +1544,14 @@ function batch<TSpec, TResult>(
             // Tell other callers to wait until we're successful again (i.e. apply backpressure)
             holdup();
             lastError = coerceError(e);
-            break;
+            // Only retry transient failures. A non-retryable error (e.g. a
+            // programming/constraint error) will never succeed, so we fail fast
+            // rather than looping `maxAttempts` times with backoff - matching
+            // `makeEnhancedWithPgClient.withRetries`. Retryable errors fall
+            // through to the next iteration (which applies the backoff delay).
+            if (!RETRYABLE_ERROR_CODES[lastError.code as string]) {
+              break;
+            }
           }
         }
         throw (