diff --git a/charger/zaptec.go b/charger/zaptec.go
index a7ca69516..43fad7506 100644
--- a/charger/zaptec.go
+++ b/charger/zaptec.go
@@ -55,6 +55,9 @@ type Zaptec struct {
 	priority   bool
 	passive    bool
 	lastStatus int
+
+	session      string    // last seen SessionIdentifier
+	sessionStart time.Time // start of the current session
 }
 
 func init() {
@@ -325,6 +328,33 @@ func (c *Zaptec) ChargedEnergy() (float64, error) {
 	return res.ObservationByID(zaptec.TotalChargePowerSession).Float64()
 }
 
+var _ api.ConnectionTimer = (*Zaptec)(nil)
+
+// ConnectionDuration implements the api.ConnectionTimer interface.
+// Derived from SessionIdentifier: a session change drops the duration, so the loadpoint detects a cable swap as reconnect.
+func (c *Zaptec) ConnectionDuration() (time.Duration, error) {
+	res, err := c.statusG.Get()
+	if err != nil {
+		return 0, err
+	}
+
+	var session string
+	if o := res.ObservationByID(zaptec.SessionIdentifier); o != nil {
+		session = o.ValueAsString
+	}
+
+	if session != c.session {
+		c.session = session
+		c.sessionStart = time.Now()
+	}
+
+	if session == "" {
+		return 0, nil
+	}
+
+	return time.Since(c.sessionStart), nil
+}
+
 var _ api.PhaseCurrents = (*Zaptec)(nil)
 
 // Currents implements the api.PhaseCurrents interface