Styv, I am very glad that rShopping List
(Google Play Link) worked better for you than the others you tried.
You do not have to kill rShopping List. It has no background processes and if you are not interacting with it, it is idle. It was originally written for the first commercial Android phone (the G1), which had very little memory and an inadequate battery. Every care has been taken to ensure that rShopping List uses as few resources as possible.
I know that when I get a shiny new app, I play with it intensively for a while. Perhaps you were having so much fun setting up your lists and configuring rShopping List just the way you like it (not to mention your shopping round) that rShopping List became your number one consumer of power.
I suspect now that you have it all setup, you will see the battery usage drop off substantially. If that doesn't happen, please let me know. You can reach me quickly through the private community for rShopping List users on Google Plus. I use it almost everyday for shopping and it is usually near the bottom of my battery statistics.
In the meantime, I hope rShopping List makes your shopping more organized, faster, and just plain better.
Thanks for your support.