I have proposal that You can put somewhere on battle screen "SAVE" button. After pressing it data of current battle (wave, chests, your HP, monsters & their HP) is saved. I have this suggestion because autosave not always work. There are a lot of autosave crashes, especially when you play on phone & you get call or must make a call in time of battle. There are some battles that take more than few minutes, on panzers for example. I had few times autosave crash during panzers & it hurts when you lose hard earned there gold chests.
It should work like this:
- you press button so your data of battle is saved (save can be made on device or on server),
- when you come back to game & see that autosave crashed you can retrive saved battle from menu, pushing for example "resume saved battle".
To be fair save made with "save button" should be deleted after you make any spin after pushing button, other way there may be abuses about chests