diff --git a/casdk-docs/docs/architecture/decisions/0016-watt-time-v3.md b/casdk-docs/docs/architecture/decisions/0016-watt-time-v3.md
index 0e726d313..a2b199c64 100644
--- a/casdk-docs/docs/architecture/decisions/0016-watt-time-v3.md
+++ b/casdk-docs/docs/architecture/decisions/0016-watt-time-v3.md
@@ -38,7 +38,7 @@ The following is configured at  `CarbonAware.DataSources.WattTime/src/Constants/
 | Forecast     | Get forecast| /forecast | /forecast   | **TODO: CHECK IMPACT** <br> No longer be used for historical data <br> _Request_ <li> `ba` is now `region` <li> `extended_forecast` removed <li> `horizon_hours` added  <li> `signal_type` added <li> Historical forecasts are now at `/forecast/historical` <br> _Response_ <li> `signal_type` added 
 | Historical   | Get historical forecast data | /historical (?) | /forecast/historical (?)           | **We need to validate why historical was being used for the API, and what historical used to be, and whether this should be the new /forecast/historical or not.**
 | Balancing Authority From Location | Get balancing authority from location | /ba-from-loc | /region-from-loc          | Check if the CA SDK uses BA at all <br><br> _Request_ <li> `name` is now `region_full_name` <li> `abbrev` is now `region` <li> `signal_type` added <br> _Response_ <li> `id` removed <li> `signal_type` added  | 
-| Login        | User login  | https://api2.watttime.org/v2/login    | https://api.watttime.org/login | Path has changed from being version specific to being unique from the API version.  <br><br> **TODO: CHECK HOW BASE URL IS DEFINED AS THIS WILL NOW HAVE DIFFERENT VALUES** 
+| Login        | User login  | https://api2.watttime.org/v2/login    | https://api.watttime.org/login | Path has changed from being version specific to being no longer related to the API version.  <br><br> **TODO: CHECK HOW BASE URL IS DEFINED AS THIS WILL NOW HAVE DIFFERENT VALUES** 
 
 ### Query Strings
 
diff --git a/src/CarbonAware.DataSources/CarbonAware.DataSources.WattTime/src/Client/IWattTimeClient.cs b/src/CarbonAware.DataSources/CarbonAware.DataSources.WattTime/src/Client/IWattTimeClient.cs
index fbe1fdef1..4cdf21f18 100644
--- a/src/CarbonAware.DataSources/CarbonAware.DataSources.WattTime/src/Client/IWattTimeClient.cs
+++ b/src/CarbonAware.DataSources/CarbonAware.DataSources.WattTime/src/Client/IWattTimeClient.cs
@@ -8,6 +8,7 @@ namespace CarbonAware.DataSources.WattTime.Client;
 internal interface IWattTimeClient
 {
     public const string NamedClient = "WattTimeClient";
+    public const string NamedAuthenticationClient = "WattTimeAuthenticationClient"
 
     /// <summary>
     /// Async method to get observed emission data for a given balancing authority and time period.
diff --git a/src/CarbonAware.DataSources/CarbonAware.DataSources.WattTime/src/Client/WattTimeClient.cs b/src/CarbonAware.DataSources/CarbonAware.DataSources.WattTime/src/Client/WattTimeClient.cs
index ed4e10e5d..9b17882ae 100644
--- a/src/CarbonAware.DataSources/CarbonAware.DataSources.WattTime/src/Client/WattTimeClient.cs
+++ b/src/CarbonAware.DataSources/CarbonAware.DataSources.WattTime/src/Client/WattTimeClient.cs
@@ -25,6 +25,7 @@ internal class WattTimeClient : IWattTimeClient
     };
 
     private HttpClient _client;
+    private HttpClient _authenticationClient;
 
     private IOptionsMonitor<WattTimeClientConfiguration> _configurationMonitor { get; }
 
@@ -37,12 +38,19 @@ internal class WattTimeClient : IWattTimeClient
     public WattTimeClient(IHttpClientFactory factory, IOptionsMonitor<WattTimeClientConfiguration> configurationMonitor, ILogger<WattTimeClient> log, IMemoryCache memoryCache)
     {
         _client = factory.CreateClient(IWattTimeClient.NamedClient);
+        _authenticationClient = factory.CreateClient(IWattTimeClient.NamedAuthenticationClient);
+
         _configurationMonitor = configurationMonitor;
         _log = log;
         _configuration.Validate();
         _client.BaseAddress = new Uri(this._configuration.BaseUrl);
         _client.DefaultRequestHeaders.Accept.Clear();
         _client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue(MediaTypeNames.Application.Json));
+        
+        _authenticationClient.BaseAddress = new Uri(this._configuration.AuthenticationBaseUrl);
+        _authenticationClient.DefaultRequestHeaders.Accept.Clear();
+        _authenticationClient.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue(MediaTypeNames.Application.Json));
+        
         _memoryCache = memoryCache;
     }
 
@@ -215,7 +223,7 @@ private async Task UpdateAuthTokenAsync()
         _log.LogInformation("Attempting to log in user {username}", this._configuration.Username);
 
         this.SetBasicAuthenticationHeader();
-        HttpResponseMessage response = await this._client.GetAsync(Paths.Login);
+        HttpResponseMessage response = await this._authenticationClient.GetAsync(Paths.Login);
 
         LoginResult? data = null;
 
@@ -239,6 +247,7 @@ private void SetBasicAuthenticationHeader()
     {
         var authToken = Encoding.UTF8.GetBytes($"{this._configuration.Username}:{this._configuration.Password}");
         this._client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue(AuthenticationHeaderTypes.Basic, Convert.ToBase64String(authToken));
+        this._authenticationClient.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue(AuthenticationHeaderTypes.Basic, Convert.ToBase64String(authToken));
     }
 
     internal void SetBearerAuthenticationHeader(string token)
diff --git a/src/CarbonAware.DataSources/CarbonAware.DataSources.WattTime/src/Configuration/WattTimeClientConfiguration.cs b/src/CarbonAware.DataSources/CarbonAware.DataSources.WattTime/src/Configuration/WattTimeClientConfiguration.cs
index 746cd2b4c..104aeb759 100644
--- a/src/CarbonAware.DataSources/CarbonAware.DataSources.WattTime/src/Configuration/WattTimeClientConfiguration.cs
+++ b/src/CarbonAware.DataSources/CarbonAware.DataSources.WattTime/src/Configuration/WattTimeClientConfiguration.cs
@@ -25,6 +25,12 @@ internal class WattTimeClientConfiguration
     /// </summary>
     public string BaseUrl { get; set; } = "https://api2.watttime.org/v2/";
 
+    /// <summary>
+    /// Authentication base url.  This changed between v2 and v3 
+    /// to be different to the API base url.
+    /// </summary>
+    public string AuthenticationBaseUrl { get; set; } = "https://api.watttime.org/";
+
     /// <summary>
     /// Gets or sets the cached expiration time (in seconds) for a BalancingAuthority instance.
     /// It defaults to 86400 secs.
@@ -51,6 +57,11 @@ public void Validate()
             throw new ConfigurationException($"{Key}:{nameof(this.BaseUrl)} is not a valid absolute url.");
         }
 
+        if (!Uri.IsWellFormedUriString(this.AuthenticationBaseUrl, UriKind.Absolute))
+        {
+            throw new ConfigurationException($"{Key}:{nameof(this.AuthenticationBaseUrl)} is not a valid absolute url.");
+        }
+
         // Validate credential encoding/decoding with UTF8
         if (!Encoding.UTF8.GetString(Encoding.UTF8.GetBytes(this.Username)).Equals(this.Username))
         {