I am relatively new to this site so please excuse teaching granny to suck eggs(sorry grannies) but, these abnormal high temperatures in the UK at the moment will have direct effect on your cycle batteries. In some cases weakening the output and in extreme cases they could explode. If you leave your bike out for any reason try to put it in the shade or if possible and practical remove it. Just a simple tip from an experienced electrical and automation engineer with over 50 years experience.