diff --git a/include/JkBmsController.h b/include/JkBmsController.h
index 0cb2e46e0..5399951d4 100644
--- a/include/JkBmsController.h
+++ b/include/JkBmsController.h
@@ -2,6 +2,7 @@
 
 #include <memory>
 #include <vector>
+#include <frozen/string.h>
 
 #include "Battery.h"
 #include "JkBmsSerialMessage.h"
@@ -30,7 +31,7 @@ class Controller : public BatteryProvider {
             FrameCompleted
         };
 
-        std::string const& getStatusText(Status status);
+        frozen::string const& getStatusText(Status status);
         void announceStatus(Status status);
         void sendRequest(uint8_t pollInterval);
         void rxData(uint8_t inbyte);
diff --git a/include/JkBmsDataPoints.h b/include/JkBmsDataPoints.h
index ccd136b75..b8c1a0b55 100644
--- a/include/JkBmsDataPoints.h
+++ b/include/JkBmsDataPoints.h
@@ -6,6 +6,8 @@
 #include <string>
 #include <unordered_map>
 #include <variant>
+#include <frozen/map.h>
+#include <frozen/string.h>
 
 namespace JkBms {
 
@@ -33,7 +35,7 @@ enum class AlarmBits : uint16_t {
 #undef ALARM_ENUM
 };
 
-static const std::map<AlarmBits, std::string> AlarmBitTexts = {
+static const frozen::map<AlarmBits, frozen::string, 16> AlarmBitTexts = {
 #define ALARM_TEXT(name, value) { AlarmBits::name, #name },
     ALARM_BITS(ALARM_TEXT)
 #undef ALARM_TEXT
@@ -51,7 +53,7 @@ enum class StatusBits : uint16_t {
 #undef STATUS_ENUM
 };
 
-static const std::map<StatusBits, std::string> StatusBitTexts = {
+static const frozen::map<StatusBits, frozen::string, 4> StatusBitTexts = {
 #define STATUS_TEXT(name, value) { StatusBits::name, #name },
     STATUS_BITS(STATUS_TEXT)
 #undef STATUS_TEXT
diff --git a/include/PowerLimiter.h b/include/PowerLimiter.h
index 40d8aa892..af6ed28f5 100644
--- a/include/PowerLimiter.h
+++ b/include/PowerLimiter.h
@@ -8,6 +8,7 @@
 #include <memory>
 #include <functional>
 #include <TaskSchedulerDeclarations.h>
+#include <frozen/string.h>
 
 #define PL_UI_STATE_INACTIVE 0
 #define PL_UI_STATE_CHARGING 1
@@ -83,7 +84,7 @@ class PowerLimiterClass {
     bool _fullSolarPassThroughEnabled = false;
     bool _verboseLogging = true;
 
-    std::string const& getStatusText(Status status);
+    frozen::string const& getStatusText(Status status);
     void announceStatus(Status status);
     bool shutdown(Status status);
     bool shutdown() { return shutdown(_lastStatus); }
diff --git a/lib/VeDirectFrameHandler/VeDirectFrameHandler.cpp b/lib/VeDirectFrameHandler/VeDirectFrameHandler.cpp
index 0c0c544e6..2978efa73 100644
--- a/lib/VeDirectFrameHandler/VeDirectFrameHandler.cpp
+++ b/lib/VeDirectFrameHandler/VeDirectFrameHandler.cpp
@@ -295,106 +295,90 @@ uint32_t VeDirectFrameHandler::getLastUpdate() const
 	return _lastUpdate;
 }
 
-template<typename T>
-String const& VeDirectFrameHandler::getAsString(std::map<T, String> const& values, T val)
-{
-	auto pos = values.find(val);
-	if (pos == values.end()) {
-		static String dummy;
-		dummy = val;
-		return dummy;
-	}
-	return pos->second;
-}
-
-template String const& VeDirectFrameHandler::getAsString(std::map<uint8_t, String> const& values, uint8_t val);
-template String const& VeDirectFrameHandler::getAsString(std::map<uint16_t, String> const& values, uint16_t val);
-template String const& VeDirectFrameHandler::getAsString(std::map<uint32_t, String> const& values, uint32_t val);
-
 /*
  * getPidAsString
  * This function returns the product id (PID) as readable text.
  */
-String VeDirectFrameHandler::veStruct::getPidAsString() const
+frozen::string const& VeDirectFrameHandler::veStruct::getPidAsString() const
 {
-	static const std::map<uint16_t, String> values = {
-		{ 0x0300, F("BlueSolar MPPT 70|15") },
-		{ 0xA040, F("BlueSolar MPPT 75|50") },
-		{ 0xA041, F("BlueSolar MPPT 150|35") },
-		{ 0xA042, F("BlueSolar MPPT 75|15") },
-		{ 0xA043, F("BlueSolar MPPT 100|15") },
-		{ 0xA044, F("BlueSolar MPPT 100|30") },
-		{ 0xA045, F("BlueSolar MPPT 100|50") },
-		{ 0xA046, F("BlueSolar MPPT 100|70") },
-		{ 0xA047, F("BlueSolar MPPT 150|100") },
-		{ 0xA049, F("BlueSolar MPPT 100|50 rev2") },
-		{ 0xA04A, F("BlueSolar MPPT 100|30 rev2") },
-		{ 0xA04B, F("BlueSolar MPPT 150|35 rev2") },
-		{ 0xA04C, F("BlueSolar MPPT 75|10") },
-		{ 0xA04D, F("BlueSolar MPPT 150|45") },
-		{ 0xA04E, F("BlueSolar MPPT 150|60") },
-		{ 0xA04F, F("BlueSolar MPPT 150|85") },
-		{ 0xA050, F("SmartSolar MPPT 250|100") },
-		{ 0xA051, F("SmartSolar MPPT 150|100") },
-		{ 0xA052, F("SmartSolar MPPT 150|85") },
-		{ 0xA053, F("SmartSolar MPPT 75|15") },
-		{ 0xA054, F("SmartSolar MPPT 75|10") },
-		{ 0xA055, F("SmartSolar MPPT 100|15") },
-		{ 0xA056, F("SmartSolar MPPT 100|30") },
-		{ 0xA057, F("SmartSolar MPPT 100|50") },
-		{ 0xA058, F("SmartSolar MPPT 150|35") },
-		{ 0xA059, F("SmartSolar MPPT 150|10 rev2") },
-		{ 0xA05A, F("SmartSolar MPPT 150|85 rev2") },
-		{ 0xA05B, F("SmartSolar MPPT 250|70") },
-		{ 0xA05C, F("SmartSolar MPPT 250|85") },
-		{ 0xA05D, F("SmartSolar MPPT 250|60") },
-		{ 0xA05E, F("SmartSolar MPPT 250|45") },
-		{ 0xA05F, F("SmartSolar MPPT 100|20") },
-		{ 0xA060, F("SmartSolar MPPT 100|20 48V") },
-		{ 0xA061, F("SmartSolar MPPT 150|45") },
-		{ 0xA062, F("SmartSolar MPPT 150|60") },
-		{ 0xA063, F("SmartSolar MPPT 150|70") },
-		{ 0xA064, F("SmartSolar MPPT 250|85 rev2") },
-		{ 0xA065, F("SmartSolar MPPT 250|100 rev2") },
-		{ 0xA066, F("BlueSolar MPPT 100|20") },
-		{ 0xA067, F("BlueSolar MPPT 100|20 48V") },
-		{ 0xA068, F("SmartSolar MPPT 250|60 rev2") },
-		{ 0xA069, F("SmartSolar MPPT 250|70 rev2") },
-		{ 0xA06A, F("SmartSolar MPPT 150|45 rev2") },
-		{ 0xA06B, F("SmartSolar MPPT 150|60 rev2") },
-		{ 0xA06C, F("SmartSolar MPPT 150|70 rev2") },
-		{ 0xA06D, F("SmartSolar MPPT 150|85 rev3") },
-		{ 0xA06E, F("SmartSolar MPPT 150|100 rev3") },
-		{ 0xA06F, F("BlueSolar MPPT 150|45 rev2") },
-		{ 0xA070, F("BlueSolar MPPT 150|60 rev2") },
-		{ 0xA071, F("BlueSolar MPPT 150|70 rev2") },
-		{ 0xA102, F("SmartSolar MPPT VE.Can 150|70") },
-		{ 0xA103, F("SmartSolar MPPT VE.Can 150|45") },
-		{ 0xA104, F("SmartSolar MPPT VE.Can 150|60") },
-		{ 0xA105, F("SmartSolar MPPT VE.Can 150|85") },
-		{ 0xA106, F("SmartSolar MPPT VE.Can 150|100") },
-		{ 0xA107, F("SmartSolar MPPT VE.Can 250|45") },
-		{ 0xA108, F("SmartSolar MPPT VE.Can 250|60") },
-		{ 0xA109, F("SmartSolar MPPT VE.Can 250|80") },
-		{ 0xA10A, F("SmartSolar MPPT VE.Can 250|85") },
-		{ 0xA10B, F("SmartSolar MPPT VE.Can 250|100") },
-		{ 0xA10C, F("SmartSolar MPPT VE.Can 150|70 rev2") },
-		{ 0xA10D, F("SmartSolar MPPT VE.Can 150|85 rev2") },
-		{ 0xA10E, F("SmartSolar MPPT VE.Can 150|100 rev2") },
-		{ 0xA10F, F("BlueSolar MPPT VE.Can 150|100") },
-		{ 0xA110, F("SmartSolar MPPT RS 450|100") },
-		{ 0xA112, F("BlueSolar MPPT VE.Can 250|70") },
-		{ 0xA113, F("BlueSolar MPPT VE.Can 250|100") },
-		{ 0xA114, F("SmartSolar MPPT VE.Can 250|70 rev2") },
-		{ 0xA115, F("SmartSolar MPPT VE.Can 250|100 rev2") },
-		{ 0xA116, F("SmartSolar MPPT VE.Can 250|85 rev2") },
-		{ 0xA381, F("BMV-712 Smart") },
-		{ 0xA382, F("BMV-710H Smart") },
-		{ 0xA383, F("BMV-712 Smart Rev2") },
-		{ 0xA389, F("SmartShunt 500A/50mV") },
-		{ 0xA38A, F("SmartShunt 1000A/50mV") },
-		{ 0xA38B, F("SmartShunt 2000A/50mV") },
-		{ 0xA3F0, F("SmartShunt 2000A/50mV" ) }
+	static constexpr frozen::map<uint16_t, frozen::string, 77> values = {
+		{ 0x0300, "BlueSolar MPPT 70|15" },
+		{ 0xA040, "BlueSolar MPPT 75|50" },
+		{ 0xA041, "BlueSolar MPPT 150|35" },
+		{ 0xA042, "BlueSolar MPPT 75|15" },
+		{ 0xA043, "BlueSolar MPPT 100|15" },
+		{ 0xA044, "BlueSolar MPPT 100|30" },
+		{ 0xA045, "BlueSolar MPPT 100|50" },
+		{ 0xA046, "BlueSolar MPPT 100|70" },
+		{ 0xA047, "BlueSolar MPPT 150|100" },
+		{ 0xA049, "BlueSolar MPPT 100|50 rev2" },
+		{ 0xA04A, "BlueSolar MPPT 100|30 rev2" },
+		{ 0xA04B, "BlueSolar MPPT 150|35 rev2" },
+		{ 0xA04C, "BlueSolar MPPT 75|10" },
+		{ 0xA04D, "BlueSolar MPPT 150|45" },
+		{ 0xA04E, "BlueSolar MPPT 150|60" },
+		{ 0xA04F, "BlueSolar MPPT 150|85" },
+		{ 0xA050, "SmartSolar MPPT 250|100" },
+		{ 0xA051, "SmartSolar MPPT 150|100" },
+		{ 0xA052, "SmartSolar MPPT 150|85" },
+		{ 0xA053, "SmartSolar MPPT 75|15" },
+		{ 0xA054, "SmartSolar MPPT 75|10" },
+		{ 0xA055, "SmartSolar MPPT 100|15" },
+		{ 0xA056, "SmartSolar MPPT 100|30" },
+		{ 0xA057, "SmartSolar MPPT 100|50" },
+		{ 0xA058, "SmartSolar MPPT 150|35" },
+		{ 0xA059, "SmartSolar MPPT 150|10 rev2" },
+		{ 0xA05A, "SmartSolar MPPT 150|85 rev2" },
+		{ 0xA05B, "SmartSolar MPPT 250|70" },
+		{ 0xA05C, "SmartSolar MPPT 250|85" },
+		{ 0xA05D, "SmartSolar MPPT 250|60" },
+		{ 0xA05E, "SmartSolar MPPT 250|45" },
+		{ 0xA05F, "SmartSolar MPPT 100|20" },
+		{ 0xA060, "SmartSolar MPPT 100|20 48V" },
+		{ 0xA061, "SmartSolar MPPT 150|45" },
+		{ 0xA062, "SmartSolar MPPT 150|60" },
+		{ 0xA063, "SmartSolar MPPT 150|70" },
+		{ 0xA064, "SmartSolar MPPT 250|85 rev2" },
+		{ 0xA065, "SmartSolar MPPT 250|100 rev2" },
+		{ 0xA066, "BlueSolar MPPT 100|20" },
+		{ 0xA067, "BlueSolar MPPT 100|20 48V" },
+		{ 0xA068, "SmartSolar MPPT 250|60 rev2" },
+		{ 0xA069, "SmartSolar MPPT 250|70 rev2" },
+		{ 0xA06A, "SmartSolar MPPT 150|45 rev2" },
+		{ 0xA06B, "SmartSolar MPPT 150|60 rev2" },
+		{ 0xA06C, "SmartSolar MPPT 150|70 rev2" },
+		{ 0xA06D, "SmartSolar MPPT 150|85 rev3" },
+		{ 0xA06E, "SmartSolar MPPT 150|100 rev3" },
+		{ 0xA06F, "BlueSolar MPPT 150|45 rev2" },
+		{ 0xA070, "BlueSolar MPPT 150|60 rev2" },
+		{ 0xA071, "BlueSolar MPPT 150|70 rev2" },
+		{ 0xA102, "SmartSolar MPPT VE.Can 150|70" },
+		{ 0xA103, "SmartSolar MPPT VE.Can 150|45" },
+		{ 0xA104, "SmartSolar MPPT VE.Can 150|60" },
+		{ 0xA105, "SmartSolar MPPT VE.Can 150|85" },
+		{ 0xA106, "SmartSolar MPPT VE.Can 150|100" },
+		{ 0xA107, "SmartSolar MPPT VE.Can 250|45" },
+		{ 0xA108, "SmartSolar MPPT VE.Can 250|60" },
+		{ 0xA109, "SmartSolar MPPT VE.Can 250|80" },
+		{ 0xA10A, "SmartSolar MPPT VE.Can 250|85" },
+		{ 0xA10B, "SmartSolar MPPT VE.Can 250|100" },
+		{ 0xA10C, "SmartSolar MPPT VE.Can 150|70 rev2" },
+		{ 0xA10D, "SmartSolar MPPT VE.Can 150|85 rev2" },
+		{ 0xA10E, "SmartSolar MPPT VE.Can 150|100 rev2" },
+		{ 0xA10F, "BlueSolar MPPT VE.Can 150|100" },
+		{ 0xA110, "SmartSolar MPPT RS 450|100" },
+		{ 0xA112, "BlueSolar MPPT VE.Can 250|70" },
+		{ 0xA113, "BlueSolar MPPT VE.Can 250|100" },
+		{ 0xA114, "SmartSolar MPPT VE.Can 250|70 rev2" },
+		{ 0xA115, "SmartSolar MPPT VE.Can 250|100 rev2" },
+		{ 0xA116, "SmartSolar MPPT VE.Can 250|85 rev2" },
+		{ 0xA381, "BMV-712 Smart" },
+		{ 0xA382, "BMV-710H Smart" },
+		{ 0xA383, "BMV-712 Smart Rev2" },
+		{ 0xA389, "SmartShunt 500A/50mV" },
+		{ 0xA38A, "SmartShunt 1000A/50mV" },
+		{ 0xA38B, "SmartShunt 2000A/50mV" },
+		{ 0xA3F0, "SmartShunt 2000A/50mV" }
 	};
 
 	return getAsString(values, PID);
diff --git a/lib/VeDirectFrameHandler/VeDirectFrameHandler.h b/lib/VeDirectFrameHandler/VeDirectFrameHandler.h
index bc6678b53..1acf56ad6 100644
--- a/lib/VeDirectFrameHandler/VeDirectFrameHandler.h
+++ b/lib/VeDirectFrameHandler/VeDirectFrameHandler.h
@@ -13,7 +13,8 @@
 
 #include <Arduino.h>
 #include <array>
-#include <map>
+#include <frozen/string.h>
+#include <frozen/map.h>
 #include <memory>
 
 #define VE_MAX_VALUE_LEN 33 // VE.Direct Protocol: max value size is 33 including /0
@@ -39,14 +40,22 @@ class VeDirectFrameHandler {
         double I = 0;                   // battery current in A
         double E = 0;                   // efficiency in percent (calculated, moving average)
 
-        String getPidAsString() const;  // product id as string
+        frozen::string const& getPidAsString() const; // product ID as string
     } veStruct;
 
     bool textRxEvent(std::string const& who, char* name, char* value, veStruct& frame);
     bool isDataValid(veStruct const& frame) const;      // return true if data valid and not outdated
 
-    template<typename T>
-    static String const& getAsString(std::map<T, String> const& values, T val);
+    template<typename T, size_t L>
+    static frozen::string const& getAsString(frozen::map<T, frozen::string, L> const& values, T val)
+    {
+        auto pos = values.find(val);
+        if (pos == values.end()) {
+            static constexpr frozen::string dummy("???");
+            return dummy;
+        }
+        return pos->second;
+    }
 
 private:
     void setLastUpdate();                     // set timestampt after successful frame read
diff --git a/lib/VeDirectFrameHandler/VeDirectMpptController.cpp b/lib/VeDirectFrameHandler/VeDirectMpptController.cpp
index 5635cd45f..5b8d6afd7 100644
--- a/lib/VeDirectFrameHandler/VeDirectMpptController.cpp
+++ b/lib/VeDirectFrameHandler/VeDirectMpptController.cpp
@@ -1,5 +1,4 @@
 #include <Arduino.h>
-#include <map>
 #include "VeDirectMpptController.h"
 
 void VeDirectMpptController::init(int8_t rx, int8_t tx, Print* msgOut, bool verboseLogging)
@@ -90,18 +89,18 @@ void VeDirectMpptController::frameValidEvent() {
  * getCsAsString
  * This function returns the state of operations (CS) as readable text.
  */
-String VeDirectMpptController::veMpptStruct::getCsAsString() const
+frozen::string const& VeDirectMpptController::veMpptStruct::getCsAsString() const
 {
-	static const std::map<uint8_t, String> values = {
-		{ 0,   F("OFF") },
-		{ 2,   F("Fault") },
-		{ 3,   F("Bulk") },
-		{ 4,   F("Absorbtion") },
-		{ 5,   F("Float") },
-		{ 7,   F("Equalize (manual)") },
-		{ 245, F("Starting-up") },
-		{ 247, F("Auto equalize / Recondition") },
-		{ 252, F("External Control") }
+	static constexpr frozen::map<uint8_t, frozen::string, 9> values = {
+		{ 0,   "OFF" },
+		{ 2,   "Fault" },
+		{ 3,   "Bulk" },
+		{ 4,   "Absorbtion" },
+		{ 5,   "Float" },
+		{ 7,   "Equalize (manual)" },
+		{ 245, "Starting-up" },
+		{ 247, "Auto equalize / Recondition" },
+		{ 252, "External Control" }
 	};
 
 	return getAsString(values, CS);
@@ -111,12 +110,12 @@ String VeDirectMpptController::veMpptStruct::getCsAsString() const
  * getMpptAsString
  * This function returns the state of MPPT (MPPT) as readable text.
  */
-String VeDirectMpptController::veMpptStruct::getMpptAsString() const
+frozen::string const& VeDirectMpptController::veMpptStruct::getMpptAsString() const
 {
-	static const std::map<uint8_t, String> values = {
-		{ 0, F("OFF") },
-		{ 1, F("Voltage or current limited") },
-		{ 2, F("MPP Tracker active") }
+	static constexpr frozen::map<uint8_t, frozen::string, 3> values = {
+		{ 0, "OFF" },
+		{ 1, "Voltage or current limited" },
+		{ 2, "MPP Tracker active" }
 	};
 
 	return getAsString(values, MPPT);
@@ -126,29 +125,29 @@ String VeDirectMpptController::veMpptStruct::getMpptAsString() const
  * getErrAsString
  * This function returns error state (ERR) as readable text.
  */
-String VeDirectMpptController::veMpptStruct::getErrAsString() const
+frozen::string const& VeDirectMpptController::veMpptStruct::getErrAsString() const
 {
-	static const std::map<uint8_t, String> values = {
-		{ 0,   F("No error") },
-		{ 2,   F("Battery voltage too high") },
-		{ 17,  F("Charger temperature too high") },
-		{ 18,  F("Charger over current") },
-		{ 19,  F("Charger current reversed") },
-		{ 20,  F("Bulk time limit exceeded") },
-		{ 21,  F("Current sensor issue(sensor bias/sensor broken)") },
-		{ 26,  F("Terminals overheated") },
-		{ 28,  F("Converter issue (dual converter models only)") },
-		{ 33,  F("Input voltage too high (solar panel)") },
-		{ 34,  F("Input current too high (solar panel)") },
-		{ 38,  F("Input shutdown (due to excessive battery voltage)") },
-		{ 39,  F("Input shutdown (due to current flow during off mode)") },
-		{ 40,  F("Input") },
-		{ 65,  F("Lost communication with one of devices") },
-		{ 67,  F("Synchronisedcharging device configuration issue") },
-		{ 68,  F("BMS connection lost") },
-		{ 116, F("Factory calibration data lost") },
-		{ 117, F("Invalid/incompatible firmware") },
-		{ 118, F("User settings invalid") }
+	static constexpr frozen::map<uint8_t, frozen::string, 20> values = {
+		{ 0,   "No error" },
+		{ 2,   "Battery voltage too high" },
+		{ 17,  "Charger temperature too high" },
+		{ 18,  "Charger over current" },
+		{ 19,  "Charger current reversed" },
+		{ 20,  "Bulk time limit exceeded" },
+		{ 21,  "Current sensor issue(sensor bias/sensor broken)" },
+		{ 26,  "Terminals overheated" },
+		{ 28,  "Converter issue (dual converter models only)" },
+		{ 33,  "Input voltage too high (solar panel)" },
+		{ 34,  "Input current too high (solar panel)" },
+		{ 38,  "Input shutdown (due to excessive battery voltage)" },
+		{ 39,  "Input shutdown (due to current flow during off mode)" },
+		{ 40,  "Input" },
+		{ 65,  "Lost communication with one of devices" },
+		{ 67,  "Synchronisedcharging device configuration issue" },
+		{ 68,  "BMS connection lost" },
+		{ 116, "Factory calibration data lost" },
+		{ 117, "Invalid/incompatible firmware" },
+		{ 118, "User settings invalid" }
 	};
 
 	return getAsString(values, ERR);
@@ -158,19 +157,19 @@ String VeDirectMpptController::veMpptStruct::getErrAsString() const
  * getOrAsString
  * This function returns the off reason (OR) as readable text.
  */
-String VeDirectMpptController::veMpptStruct::getOrAsString() const
+frozen::string const& VeDirectMpptController::veMpptStruct::getOrAsString() const
 {
-	static const std::map<uint32_t, String> values = {
-		{ 0x00000000, F("Not off") },
-		{ 0x00000001, F("No input power") },
-		{ 0x00000002, F("Switched off (power switch)") },
-		{ 0x00000004, F("Switched off (device moderegister)") },
-		{ 0x00000008, F("Remote input") },
-		{ 0x00000010, F("Protection active") },
-		{ 0x00000020, F("Paygo") },
-		{ 0x00000040, F("BMS") },
-		{ 0x00000080, F("Engine shutdown detection") },
-		{ 0x00000100, F("Analysing input voltage") }
+	static constexpr frozen::map<uint32_t, frozen::string, 10> values = {
+		{ 0x00000000, "Not off" },
+		{ 0x00000001, "No input power" },
+		{ 0x00000002, "Switched off (power switch)" },
+		{ 0x00000004, "Switched off (device moderegister)" },
+		{ 0x00000008, "Remote input" },
+		{ 0x00000010, "Protection active" },
+		{ 0x00000020, "Paygo" },
+		{ 0x00000040, "BMS" },
+		{ 0x00000080, "Engine shutdown detection" },
+		{ 0x00000100, "Analysing input voltage" }
 	};
 
 	return getAsString(values, OR);
diff --git a/lib/VeDirectFrameHandler/VeDirectMpptController.h b/lib/VeDirectFrameHandler/VeDirectMpptController.h
index 04e0d8ca4..158772373 100644
--- a/lib/VeDirectFrameHandler/VeDirectMpptController.h
+++ b/lib/VeDirectFrameHandler/VeDirectMpptController.h
@@ -59,10 +59,10 @@ class VeDirectMpptController : public VeDirectFrameHandler {
         double H22;                     // yield yesterday kWh
         int32_t H23;                    // maximum power yesterday W
 
-        String getMpptAsString() const; // state of mppt as string
-        String getCsAsString() const;   // current state as string
-        String getErrAsString() const;  // error state as string
-        String getOrAsString() const;   // off reason as string
+        frozen::string const& getMpptAsString() const; // state of mppt as string
+        frozen::string const& getCsAsString() const;   // current state as string
+        frozen::string const& getErrAsString() const;  // error state as string
+        frozen::string const& getOrAsString() const;   // off reason as string
     };
 
     using spData_t = std::shared_ptr<veMpptStruct const>;
diff --git a/src/BatteryStats.cpp b/src/BatteryStats.cpp
index 9e975a9c6..c2c9d9d02 100644
--- a/src/BatteryStats.cpp
+++ b/src/BatteryStats.cpp
@@ -277,7 +277,7 @@ void JkBmsBatteryStats::mqttPublish() const
         for (auto iter = JkBms::AlarmBitTexts.begin(); iter != JkBms::AlarmBitTexts.end(); ++iter) {
             auto bit = iter->first;
             String value = (*oAlarms & static_cast<uint16_t>(bit))?"1":"0";
-            MqttSettings.publish(String("battery/alarms/") + iter->second.c_str(), value);
+            MqttSettings.publish(String("battery/alarms/") + iter->second.data(), value);
         }
     }
 
@@ -286,7 +286,7 @@ void JkBmsBatteryStats::mqttPublish() const
         for (auto iter = JkBms::StatusBitTexts.begin(); iter != JkBms::StatusBitTexts.end(); ++iter) {
             auto bit = iter->first;
             String value = (*oStatus & static_cast<uint16_t>(bit))?"1":"0";
-            MqttSettings.publish(String("battery/status/") + iter->second.c_str(), value);
+            MqttSettings.publish(String("battery/status/") + iter->second.data(), value);
         }
     }
 
@@ -338,7 +338,7 @@ void VictronSmartShuntStats::updateFrom(VeDirectShuntController::veShuntStruct c
     _SoC = shuntData.SOC / 10;
     _voltage = shuntData.V;
     _current = shuntData.I;
-    _modelName = shuntData.getPidAsString();
+    _modelName = shuntData.getPidAsString().data();
     _chargeCycles = shuntData.H4;
     _timeToGo = shuntData.TTG / 60;
     _chargedEnergy = shuntData.H18 / 100;
diff --git a/src/JkBmsController.cpp b/src/JkBmsController.cpp
index 2422d6d28..9282b56bd 100644
--- a/src/JkBmsController.cpp
+++ b/src/JkBmsController.cpp
@@ -5,7 +5,7 @@
 #include "MessageOutput.h"
 #include "JkBmsDataPoints.h"
 #include "JkBmsController.h"
-#include <map>
+#include <frozen/map.h>
 
 //#define JKBMS_DUMMY_SERIAL
 
@@ -255,11 +255,11 @@ Controller::Interface Controller::getInterface() const
     return Interface::Invalid;
 }
 
-std::string const& Controller::getStatusText(Controller::Status status)
+frozen::string const& Controller::getStatusText(Controller::Status status)
 {
-    static const std::string missing =  "programmer error: missing status text";
+    static constexpr frozen::string missing = "programmer error: missing status text";
 
-    static const std::map<Status, const std::string> texts = {
+    static constexpr frozen::map<Status, frozen::string, 6> texts = {
         { Status::Timeout, "timeout wating for response from BMS" },
         { Status::WaitingForPollInterval, "waiting for poll interval to elapse" },
         { Status::HwSerialNotAvailableForWrite, "UART is not available for writing" },
@@ -279,7 +279,7 @@ void Controller::announceStatus(Controller::Status status)
     if (_lastStatus == status && millis() < _lastStatusPrinted + 10 * 1000) { return; }
 
     MessageOutput.printf("[%11.3f] JK BMS: %s\r\n",
-        static_cast<double>(millis())/1000, getStatusText(status).c_str());
+        static_cast<double>(millis())/1000, getStatusText(status).data());
 
     _lastStatus = status;
     _lastStatusPrinted = millis();
diff --git a/src/MqttHandleVedirect.cpp b/src/MqttHandleVedirect.cpp
index e5997dc98..af659f0d7 100644
--- a/src/MqttHandleVedirect.cpp
+++ b/src/MqttHandleVedirect.cpp
@@ -69,7 +69,7 @@ void MqttHandleVedirectClass::loop()
         topic.concat("/");
 
         if (_PublishFull || spMpptData->PID != _kvFrame.PID)
-            MqttSettings.publish(topic + "PID", spMpptData->getPidAsString());
+            MqttSettings.publish(topic + "PID", spMpptData->getPidAsString().data());
         if (_PublishFull || strcmp(spMpptData->SER, _kvFrame.SER) != 0)
             MqttSettings.publish(topic + "SER", spMpptData->SER );
         if (_PublishFull || strcmp(spMpptData->FW, _kvFrame.FW) != 0)
@@ -77,13 +77,13 @@ void MqttHandleVedirectClass::loop()
         if (_PublishFull || spMpptData->LOAD != _kvFrame.LOAD)
             MqttSettings.publish(topic + "LOAD", spMpptData->LOAD == true ? "ON": "OFF");
         if (_PublishFull || spMpptData->CS != _kvFrame.CS)
-            MqttSettings.publish(topic + "CS", spMpptData->getCsAsString());
+            MqttSettings.publish(topic + "CS", spMpptData->getCsAsString().data());
         if (_PublishFull || spMpptData->ERR != _kvFrame.ERR)
-            MqttSettings.publish(topic + "ERR", spMpptData->getErrAsString());
+            MqttSettings.publish(topic + "ERR", spMpptData->getErrAsString().data());
         if (_PublishFull || spMpptData->OR != _kvFrame.OR)
-            MqttSettings.publish(topic + "OR", spMpptData->getOrAsString());
+            MqttSettings.publish(topic + "OR", spMpptData->getOrAsString().data());
         if (_PublishFull || spMpptData->MPPT != _kvFrame.MPPT)
-            MqttSettings.publish(topic + "MPPT", spMpptData->getMpptAsString());
+            MqttSettings.publish(topic + "MPPT", spMpptData->getMpptAsString().data());
         if (_PublishFull || spMpptData->HSDS != _kvFrame.HSDS) {
             value = spMpptData->HSDS;
             MqttSettings.publish(topic + "HSDS", value);
diff --git a/src/PowerLimiter.cpp b/src/PowerLimiter.cpp
index 86cb2751b..0efc49fa3 100644
--- a/src/PowerLimiter.cpp
+++ b/src/PowerLimiter.cpp
@@ -14,7 +14,7 @@
 #include "MessageOutput.h"
 #include <ctime>
 #include <cmath>
-#include <map>
+#include <frozen/map.h>
 
 PowerLimiterClass PowerLimiter;
 
@@ -26,11 +26,11 @@ void PowerLimiterClass::init(Scheduler& scheduler)
     _loopTask.enable();
 }
 
-std::string const& PowerLimiterClass::getStatusText(PowerLimiterClass::Status status)
+frozen::string const& PowerLimiterClass::getStatusText(PowerLimiterClass::Status status)
 {
-    static const std::string missing =  "programmer error: missing status text";
+    static const frozen::string missing = "programmer error: missing status text";
 
-    static const std::map<Status, const std::string> texts = {
+    static const frozen::map<Status, frozen::string, 19> texts = {
         { Status::Initializing, "initializing (should not see me)" },
         { Status::DisabledByConfig, "disabled by configuration" },
         { Status::DisabledByMqtt, "disabled by MQTT" },
@@ -70,7 +70,7 @@ void PowerLimiterClass::announceStatus(PowerLimiterClass::Status status)
     if (status == Status::DisabledByConfig && _lastStatus == status) { return; }
 
     MessageOutput.printf("[%11.3f] DPL: %s\r\n",
-        static_cast<double>(millis())/1000, getStatusText(status).c_str());
+        static_cast<double>(millis())/1000, getStatusText(status).data());
 
     _lastStatus = status;
     _lastStatusPrinted = millis();