refactor: Extract default batch size into kernel

diff --git a/src/init.cpp b/src/init.cpp
index b6b52e2c..b29a2634 100644
--- a/src/init.cpp
+++ b/src/init.cpp
@@ -496,7 +496,7 @@ void SetupServerArgs(ArgsManager& argsman, bool can_listen_ipc)
     argsman.AddArg("-coinstatsindex", strprintf("Maintain coinstats index used by the gettxoutsetinfo RPC (default: %u)", DEFAULT_COINSTATSINDEX), ArgsManager::ALLOW_ANY, OptionsCategory::OPTIONS);
     argsman.AddArg("-conf=<file>", strprintf("Specify path to read-only configuration file. Relative paths will be prefixed by datadir location (only useable from command line, not configuration file) (default: %s)", BITCOIN_CONF_FILENAME), ArgsManager::ALLOW_ANY, OptionsCategory::OPTIONS);
     argsman.AddArg("-datadir=<dir>", "Specify data directory", ArgsManager::ALLOW_ANY | ArgsManager::DISALLOW_NEGATION, OptionsCategory::OPTIONS);
-    argsman.AddArg("-dbbatchsize", strprintf("Maximum database write batch size in bytes (default: %u)", nDefaultDbBatchSize), ArgsManager::ALLOW_ANY | ArgsManager::DEBUG_ONLY, OptionsCategory::OPTIONS);
+    argsman.AddArg("-dbbatchsize", strprintf("Maximum database write batch size in bytes (default: %u)", DEFAULT_DB_CACHE_BATCH), ArgsManager::ALLOW_ANY | ArgsManager::DEBUG_ONLY, OptionsCategory::OPTIONS);
     argsman.AddArg("-dbcache=<n>", strprintf("Maximum database cache size <n> MiB (minimum %d, default: %d). Make sure you have enough RAM. In addition, unused memory allocated to the mempool is shared with this cache (see -maxmempool).", MIN_DB_CACHE >> 20, DEFAULT_DB_CACHE >> 20), ArgsManager::ALLOW_ANY, OptionsCategory::OPTIONS);
     argsman.AddArg("-includeconf=<file>", "Specify additional configuration file, relative to the -datadir path (only useable from configuration file, not command line)", ArgsManager::ALLOW_ANY, OptionsCategory::OPTIONS);
     argsman.AddArg("-allowignoredconf", strprintf("For backwards compatibility, treat an unused %s file in the datadir as a warning, not an error.", BITCOIN_CONF_FILENAME), ArgsManager::ALLOW_ANY, OptionsCategory::OPTIONS);
diff --git a/src/kernel/caches.h b/src/kernel/caches.h
index 33ae6047..63bb44c5 100644
--- a/src/kernel/caches.h
+++ b/src/kernel/caches.h
@@ -11,6 +11,9 @@
 
 //! Suggested default amount of cache reserved for the kernel (bytes)
 static constexpr size_t DEFAULT_KERNEL_CACHE{450_MiB};
+//! Default LevelDB write batch size
+static constexpr size_t DEFAULT_DB_CACHE_BATCH{16_MiB};
+
 //! Max memory allocated to block tree DB specific cache (bytes)
 static constexpr size_t MAX_BLOCK_DB_CACHE{2_MiB};
 //! Max memory allocated to coin DB specific cache (bytes)
diff --git a/src/txdb.h b/src/txdb.h
index 968b7c27..ea0cf9d7 100644
--- a/src/txdb.h
+++ b/src/txdb.h
@@ -8,6 +8,7 @@
 
 #include <coins.h>
 #include <dbwrapper.h>
+#include <kernel/caches.h>
 #include <kernel/cs_main.h>
 #include <sync.h>
 #include <util/fs.h>
@@ -21,16 +22,12 @@
 class COutPoint;
 class uint256;
 
-//! -dbbatchsize default (bytes)
-static const int64_t nDefaultDbBatchSize = 16 << 20;
-
 //! User-controlled performance and debug options.
 struct CoinsViewOptions {
     //! Maximum database write batch size in bytes.
-    size_t batch_write_bytes = nDefaultDbBatchSize;
-    //! If non-zero, randomly exit when the database is flushed with (1/ratio)
-    //! probability.
-    int simulate_crash_ratio = 0;
+    size_t batch_write_bytes{DEFAULT_DB_CACHE_BATCH};
+    //! If non-zero, randomly exit when the database is flushed with (1/ratio) probability.
+    int simulate_crash_ratio{0};
 };
 
 /** CCoinsView backed by the coin database (chainstate/) */