Thank you very much everyone for all your replies.
I’m fairly sure I don’t have accidental damage insurance cover.
Also, I’m fairly sure dropping it in water would invalidate the warranty, so I’m not even thinking about warranty cover – just whether it may still be repairable.
I don’t really want to try changing the battery again, as I meticulously tried following one of the YouTube videos with my previous iPhone after it started losing its charge, and ended up damaging it, as one of the tiny screws inside wouldn’t come out, but kept turning endlessly. I can’t actually remember what happened now, but in my frustration I think I broke a tiny piece off, so the phone was fit for the garbage. I bought the kit online.
I have to confess that I did put this phone on the radiator for a few minutes after giving it a good shake and wipe down (having taken the sim out), which probably wasn’t the brightest thing to do, as they don’t like high temperatures. I quickly removed it and then left it alone for a couple or hours. Some time later, I noticed, on touching it, that it was red hot – which may indicate a fault inside. I did pick it out of the water very quickly, but even a small amount can damage it.
It’s currently sitting in a plastic bag of rice, which was what colleagues at work told me to do (despite online advice not to). I thought it unlikely to do any harm, even if it doesn’t do any good.
I’ll take another look at it in the morning and try to give it another charge, then think what to do. I believe I need an appointment to go to any Apple store – and the Bromley one gets loads of bad reviews for customer service.
It’s an iPhone 4SE by the way.