Hi Jason,
I had lots of problems before I changed my battery, similar to yours.
She would be fine unless I left her for a couple of days, I had heard about RF problems but did not want to buy an expensive part only to find it was not that at all.
So I waited for the next service, meanwhile she went flat again unable to use remote etc. but had enough power to open doors manualy and keep the radio codes etc.
Put her on charge with my old charger and same again, flat in a day or so.
The garage said probably battery or even your old charger not good enough for the size of battery. They were right on both counts, battery had an internal fault and the old charger would not achieve full charge any way.
Replaced the battery several months ago and not had any problems since.
May I suggest you get a genuine battery as mine was only the same price as a Halfords, my garage fitted it free and I did not need any codes reset.
I hope this helps
Fred