It would be difficult for anyone to know why your battery exploded unless careful examination of the internals is undertaken by a battery expert. That is if the internals can still be found.
There could be a number of reasons for the failure.
What you should ask yourself is just how intelligent or safe-in-opertaion a circa £11 charger is likely to be. I personally would not trust one at all because there are a lot of very cheap far-eastern semiconductors and electronic devices being sold which do not provide reliable service. For example, there are PC power supplies being sold at very low prices which are dangerous and also damage PC components. Some lack basic safety and protection features.
I would only trust an intelligent charger from one of the major manufacturers - CTEK, Optimate, NOCO being three really well known brands. If I did not wish to invest in such a quality but expensive product, I would buy an old fashioned simple charger and apply human intelligence to the charging process.
You should not assume that all intelligent chargers have the same level of intelligence. Some of them may have none!