After a certain amount, the money counter just kinda stops at a number, that number is "9,223,372,036,854,775,807". Its kinda difficult to determin how many upgrades I can buy; so I have a suggestion. Make the numbers smaller, like once you get to a million, change it to 1M, 1.1M etc, and have that the basis of numbers, as they get bigger.
To be honest, I think you should keep the Energy system the way it is. As another coment said; stocks are a much better way of getting money. But if I have one thing I'd like to see; it's more stock options, perhaps a few that could be a bit more unpredictable, because after a while you can see the pattern in the normal stocks.
But aside from that; its a good game.
Keep up the great work!
Just an Idea I think would be helpful; A "Sell All" button. Due to the fact I left this on whilst I was at college, and when I came back I must have spent over 30 minutes just click to sell everything I had. Something as simple as that could be quite the game changer. Thanks for taking to time to read this.
~JamesF
If you ever add achievements; which you hopefully will, I'd love it if you added an achievement for the Red Balloons. How about where you have to kill 99 of them, in reference to the song: "99 Red Balloons". Just an idea, your choice to implement it or not. Good game too, it's quite fun! :)
 "Auto Turret"){kind=icon}
 "Mystery Idle"){kind=icon}
![Play Money Makers [BETA]](https://cdn3.kongcdn.com/game_icons/0054/4025/logo.png?i10c=img.resize(width:250) "Money Makers [BETA]"){kind=icon}
 "Idle Fish"){kind=icon}
 "Ninja Battle Idle"){kind=icon}
 "Idle Mine"){kind=icon}
 "Idle Woodcutting"){kind=icon}
Achievements seem like a good idea, the next update may very well include them!