Finish the title in Extreme mode, with only 3 saves available is really a nuisance, then the fact of finding a derisory amount of Medikit and Ammunition, make this mode even more difficult, fortunately comes to our aid a "dirty" trick that will allow us to have, slowly, the infinite credits, so you can buy Energy Nodes, Ammunition, Medikit or whatever you need to complete the Extreme Mode, the only flaw in this trick is that you must have at least one DLC and then spend real credits!!!
TRICK - INFINITE CREDITS
You will have to buy one or two dlc (the ones that contain the special versions of the Detonator, so either Martial Law or Supernova which is more recommended than Martial Law because at the same price you get more stuff! ).
At the first store of the game you'll get the Detonator for free (or you'll get 2 if you have 2 dlc), exit the store, shoot all the mines and deactivate them. Go back to the store, sell the Detonator unloaded. Buy it again (always for free), leave the store and shoot the mines and deactivate them and so on as you want!
The mines that you collect can be sold forever, they are worth 200 credits each. It 's a slow method is true ... but it gives you the opportunity to buy everything you want and buy as many energy knots you want ( A nice help for the maximum mode! )
It will not be the same a walk to finish the maximum mode, but it's not a bad trick, right?
Too bad you have to spend some real money for DLC!
For the moment this is the only trick there is, but hopefully in the future we'll discover other much faster ones!
I remind you that we have made the complete guide to the game