If cranking speed is slow, then ether can make the engine harder to start. A good load test on the battery is needed. A tester over 100 amp load will check the battery correctly. Small testers don't give reliable results. Replace and corroded cables. If you see any corrosion on the outside, more can be inside were you can't see it. If you can add a jump start battery, connect to the starter terminals. If cranking speed is normal then your problem is in the cables. If you jump connect at the battery and cranking is normal, then it is just a battery. If nothing changes, it might be the starter.
Be sure to check for hydraulics loading the hydraulic pump. You don't want any lever to be sticking, causing the hydraulic pump to load the engine when cranking.
This could be an issue since you said it stalls the engine. Case uses a gear pump so, it does not have any regulators to worry about.
Look for auxiliary controls that you don't normally use to be the problem. If it has an electric control for hammer attachments, check for it loading the engine.
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