diff --git a/casanovo/config.yaml b/casanovo/config.yaml
index ffb9bf45..74d6b782 100644
--- a/casanovo/config.yaml
+++ b/casanovo/config.yaml
@@ -63,8 +63,8 @@ max_mods: 1
 # where aa is a standard amino acid (or "nterm" for an N-terminal mod)
 # and mod_residue is a key from the "residues" dictionary.
 # Example: "M:M+15.995,nterm:+43.006"
-allowed_fixed_mods: "C:C+57.021"
-allowed_var_mods: "M:M+15.995,N:N+0.984,Q:Q+0.984,nterm:+42.011,nterm:+43.006,nterm:-17.027,nterm:+43.006-17.027"
+allowed_fixed_mods: "C:C[Carbamidomethyl]"
+allowed_var_mods: "M:M[Oxidation],N:N[Deamidated],Q:Q[Deamidated],nterm:[Acetyl]-,nterm:[Carbamyl]-,nterm:[Ammonia-loss]-,nterm:[+25.980265]-"
 
 
 ###
diff --git a/casanovo/denovo/model.py b/casanovo/denovo/model.py
index 69730ed2..53c6a9a0 100644
--- a/casanovo/denovo/model.py
+++ b/casanovo/denovo/model.py
@@ -1288,8 +1288,8 @@ def _pep_batch_ready(self, num_candidate_psms: int) -> bool:
             True if the batch is ready, False otherwise.
         """
         return (
-            num_candidate_psms % self.psm_batch_size
-        ) == self.psm_batch_size - 1
+            num_candidate_psms % self.psm_batch_size == 0
+        ) and num_candidate_psms != 0
 
     def _initialize_psm_batch(self, batch: Dict[str, Any]) -> Dict[str, List]:
         """
diff --git a/tests/test_integration.py b/tests/test_integration.py
index b5adfa96..948cff63 100644
--- a/tests/test_integration.py
+++ b/tests/test_integration.py
@@ -6,7 +6,6 @@
 from click.testing import CliRunner
 
 from casanovo import casanovo
-from casanovo.config import Config
 
 TEST_DIR = Path(__file__).resolve().parent
 
diff --git a/tests/unit_tests/test_unit.py b/tests/unit_tests/test_unit.py
index 05fe5a11..d5458d84 100644
--- a/tests/unit_tests/test_unit.py
+++ b/tests/unit_tests/test_unit.py
@@ -5,6 +5,7 @@
 import hashlib
 import heapq
 import io
+import math
 import os
 import pathlib
 import platform
@@ -26,10 +27,16 @@
 import torch
 
 from casanovo import casanovo, utils
+from casanovo.config import Config
 from casanovo.data import db_utils, ms_io
 from casanovo.denovo.dataloaders import DeNovoDataModule
 from casanovo.denovo.evaluate import aa_match, aa_match_batch, aa_match_metrics
-from casanovo.denovo.model import Spec2Pep, _aa_pep_score, _calc_match_score
+from casanovo.denovo.model import (
+    DbSpec2Pep,
+    Spec2Pep,
+    _aa_pep_score,
+    _calc_match_score,
+)
 
 
 def test_version():
@@ -1008,13 +1015,104 @@ def test_digest_fasta_enzyme(tiny_fasta_file):
         ),
         tokenizer=depthcharge.tokenizers.PeptideTokenizer.from_massivekb(),
     )
-    peptide_list = pdb.db_peptides.index.to_list()
+    assert pdb.db_peptides.index.to_list() == expected_nonspecific
 
-    first = peptide_list[:50]
-    second = peptide_list[50:100]
-    third = peptide_list[100:]
 
-    assert pdb.db_peptides.index.to_list() == expected_nonspecific
+def test_psm_batches(tiny_config):
+    peptides_one = [
+        "SGSGSG",
+        "GSGSGT",
+        "SGSGTD",
+        "FSGSGS",
+        "ATSIPA",
+        "GASTRA",
+        "LSLSPG",
+        "ASQSVS",
+        "GSGTDF",
+        "SLSPGE",
+        "AQLLFL",
+        "QPEDFA",
+    ]
+
+    peptides_two = [
+        "SQSVSS",
+        "KPGQAP",
+        "SPPTLS",
+        "ASTRAT",
+        "RFSGSG",
+        "IYGAST",
+        "APAQLL",
+        "PTLSLS",
+        "TLSLSP",
+        "TLTISS",
+        "WYQQKP",
+        "TWYQQK",
+    ]
+
+    def mock_get_candidates(precursor_mz, precorsor_charge):
+        if precorsor_charge == 1:
+            return pd.Series(peptides_one)
+        elif precorsor_charge == 2:
+            return pd.Series(peptides_two)
+        else:
+            return pd.Series()
+
+    tokenizer = depthcharge.tokenizers.peptides.PeptideTokenizer(
+        residues=Config(tiny_config).residues
+    )
+    db_model = DbSpec2Pep(tokenizer=tokenizer)
+    db_model.protein_database = unittest.mock.MagicMock()
+    db_model.protein_database.get_candidates = mock_get_candidates
+
+    mock_batch = {
+        "precursor_mz": torch.Tensor([42.0, 84.0, 126.0]),
+        "precursor_charge": torch.Tensor([1, 2, 3]),
+        "peak_file": ["one.mgf", "two.mgf", "three.mgf"],
+        "scan_id": [1, 2, 3],
+    }
+
+    expected_batch_all = {
+        "precursor_mz": torch.Tensor([42.0] * 12 + [84.0] * 12),
+        "precursor_charge": torch.Tensor([1] * 12 + [2] * 12),
+        "seq": tokenizer.tokenize(peptides_one + peptides_two),
+        "peak_file": ["one.mgf"] * 12 + ["two.mgf"] * 12,
+        "scan_id": [1] * 12 + [2] * 12,
+    }
+
+    for psm_batch_size in [24, 12, 8, 10]:
+        db_model.psm_batch_size = psm_batch_size
+        psm_batches = list(db_model._psm_batches(mock_batch))
+        assert len(psm_batches) == math.ceil(24 / psm_batch_size)
+        num_spectra = 0
+
+        for psm_batch in psm_batches:
+            end_idx = min(
+                num_spectra + psm_batch_size,
+                len(expected_batch_all["peak_file"]),
+            )
+            assert torch.allclose(
+                psm_batch["precursor_mz"],
+                expected_batch_all["precursor_mz"][num_spectra:end_idx],
+            )
+            assert torch.equal(
+                psm_batch["precursor_charge"],
+                expected_batch_all["precursor_charge"][num_spectra:end_idx],
+            )
+            assert torch.equal(
+                psm_batch["seq"],
+                expected_batch_all["seq"][num_spectra:end_idx],
+            )
+            assert (
+                psm_batch["peak_file"]
+                == expected_batch_all["peak_file"][num_spectra:end_idx]
+            )
+            assert (
+                psm_batch["scan_id"]
+                == expected_batch_all["scan_id"][num_spectra:end_idx]
+            )
+            num_spectra += len(psm_batch["peak_file"])
+
+        assert num_spectra == 24
 
 
 def test_get_candidates(tiny_fasta_file):