diff --git a/meter/fritz/aha/aha.go b/meter/fritz/aha/aha.go
index e98542f47..8341585b4 100644
--- a/meter/fritz/aha/aha.go
+++ b/meter/fritz/aha/aha.go
@@ -6,7 +6,6 @@ import (
 	"net/url"
 	"strconv"
 	"strings"
-	"time"
 
 	"github.com/evcc-io/evcc/api"
 	"github.com/evcc-io/evcc/meter/fritz"
@@ -23,8 +22,6 @@ import (
 type Connection struct {
 	*request.Helper
 	*fritz.Settings
-	SID     string
-	updated time.Time
 }
 
 // NewConnection creates FritzDECT connection
@@ -58,19 +55,13 @@ func NewConnection(uri, ain, user, password string) (*Connection, error) {
 
 // ExecCmd execautes an FritzDECT AHA-HTTP-Interface command
 func (c *Connection) ExecCmd(function string) (string, error) {
-	// refresh Fritzbox session id
-	if time.Since(c.updated) >= fritz.SessionTimeout {
-		sid, err := c.GetSessionID(c.Helper)
-		if err != nil {
-			return "", err
-		}
-		// update session timestamp
-		c.SID = sid
-		c.updated = time.Now()
+	sid, err := c.GetSessionID(c.Helper)
+	if err != nil {
+		return "", err
 	}
 
 	parameters := url.Values{
-		"sid":       {c.SID},
+		"sid":       {sid},
 		"ain":       {c.AIN},
 		"switchcmd": {function},
 	}
diff --git a/meter/fritz/smarthome/smarthome.go b/meter/fritz/smarthome/smarthome.go
index 624af3daf..e65647192 100644
--- a/meter/fritz/smarthome/smarthome.go
+++ b/meter/fritz/smarthome/smarthome.go
@@ -21,10 +21,8 @@ import (
 type Connection struct {
 	*request.Helper
 	*fritz.Settings
-	SID     string
-	UID     string // device UID (AIN with space)
-	updated time.Time
-	unitG   util.Cacheable[Unit]
+	UID   string // device UID (AIN with space)
+	unitG util.Cacheable[Unit]
 }
 
 // NewConnection creates a new REST API connection
@@ -75,7 +73,8 @@ func ainToUID(ain string) string {
 
 // getUnit fetches unit data from REST API
 func (c *Connection) getUnit() (Unit, error) {
-	if err := c.refreshSession(); err != nil {
+	sid, err := c.GetSessionID(c.Helper)
+	if err != nil {
 		return Unit{}, err
 	}
 
@@ -83,7 +82,7 @@ func (c *Connection) getUnit() (Unit, error) {
 	uri := fmt.Sprintf("%s/api/v0/smarthome/overview/units/%s", c.URI, url.PathEscape(c.UID))
 
 	req, _ := request.New("GET", uri, nil, map[string]string{
-		"Authorization": "AVM-SID " + c.SID,
+		"Authorization": "AVM-SID " + sid,
 	}, request.AcceptJSON)
 
 	var unit Unit
@@ -101,10 +100,15 @@ func (c *Connection) getUnit() (Unit, error) {
 
 // findUnit searches for our unit in the list of all units
 func (c *Connection) findUnit() (Unit, error) {
+	sid, err := c.GetSessionID(c.Helper)
+	if err != nil {
+		return Unit{}, err
+	}
+
 	uri := fmt.Sprintf("%s/api/v0/smarthome/overview/units", c.URI)
 
 	req, err := request.New("GET", uri, nil, map[string]string{
-		"Authorization": "AVM-SID " + c.SID,
+		"Authorization": "AVM-SID " + sid,
 	}, request.AcceptJSON)
 	if err != nil {
 		return Unit{}, err
@@ -201,7 +205,8 @@ func (c *Connection) SwitchOff() error {
 
 // setSwitch sets the switch state via REST API
 func (c *Connection) setSwitch(on bool) error {
-	if err := c.refreshSession(); err != nil {
+	sid, err := c.GetSessionID(c.Helper)
+	if err != nil {
 		return err
 	}
 
@@ -219,7 +224,7 @@ func (c *Connection) setSwitch(on bool) error {
 	}
 
 	req, _ := request.New("PUT", uri, request.MarshalJSON(data), map[string]string{
-		"Authorization": "AVM-SID " + c.SID,
+		"Authorization": "AVM-SID " + sid,
 	}, request.JSONEncoding)
 
 	var unit Unit
@@ -240,19 +245,3 @@ func (c *Connection) setSwitch(on bool) error {
 
 	return nil
 }
-
-// refreshSession ensures we have a valid session ID
-func (c *Connection) refreshSession() error {
-	// refresh Fritzbox session id
-	if time.Since(c.updated) >= fritz.SessionTimeout {
-		sid, err := c.GetSessionID(c.Helper)
-		if err != nil {
-			return err
-		}
-		// update session timestamp
-		c.SID = sid
-		c.updated = time.Now()
-	}
-
-	return nil
-}
diff --git a/meter/fritz/types.go b/meter/fritz/types.go
index 7b5599517..219970fde 100644
--- a/meter/fritz/types.go
+++ b/meter/fritz/types.go
@@ -7,6 +7,7 @@ import (
 	"errors"
 	"fmt"
 	"net/url"
+	"sync"
 	"time"
 
 	"github.com/evcc-io/evcc/util/request"
@@ -20,12 +21,24 @@ const SessionTimeout = 15 * time.Minute
 type Settings struct {
 	URI, AIN, User, Password string
 	Firmware82               bool // use new REST API (FritzOS 8.2+)
+
+	mu      sync.Mutex
+	sid     string
+	updated time.Time
 }
 
 // Fritzbox helpers (credits to https://github.com/rsdk/ahago)
 
-// getSessionID fetches a session-id based on the username and password in the connection struct
-func (s Settings) GetSessionID(c *request.Helper) (string, error) {
+// GetSessionID returns a valid Fritzbox session ID, refreshing it when the
+// previously fetched session has timed out.
+func (s *Settings) GetSessionID(c *request.Helper) (string, error) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	if time.Since(s.updated) < SessionTimeout {
+		return s.sid, nil
+	}
+
 	uri := fmt.Sprintf("%s/login_sid.lua", s.URI)
 	body, err := c.GetBody(uri)
 	if err != nil {
@@ -53,11 +66,17 @@ func (s Settings) GetSessionID(c *request.Helper) (string, error) {
 		}
 	}
 
-	return v.SID, err
+	if err != nil {
+		return "", err
+	}
+
+	s.sid = v.SID
+	s.updated = time.Now()
+	return v.SID, nil
 }
 
 // createChallengeResponse creates the Fritzbox challenge response string
-func (s Settings) createChallengeResponse(challenge string) (string, error) {
+func (s *Settings) createChallengeResponse(challenge string) (string, error) {
 	encoder := unicode.UTF16(unicode.LittleEndian, unicode.IgnoreBOM).NewEncoder()
 	utf16le, err := encoder.String(challenge + "-" + s.Password)
 	if err != nil {