This is my first post on this forum. I was looking around Wanstone HAA Battery near Dover which is something I've done many times, and I found this graffiti on said HAA unit. I Googled it and it sent me here. Hope it's of some use to you although it's been two years since you posted your original question.
Been a complete age since I have logged in here and checked anything. I would just like to say thank you for posting the above photo. Has given me a bit more interest to try and find out anything concerning the battery.