You can try to power off the phone and charge it. It will bypass any rom/kernel issues. If it still charges to 75% the it's most likely a hardware issue - battery or charging circuit.
You can also try boeffla kernel with power safeguards off.
I don't have another battery. :/
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2 days ago with version 2.6 and original kernel I started being able to only charge my phone to ~75%. I updated to 3.6 and also boeffa kernel, but the problem remains. I didn't do anything odd, that I can remember, to achieve this.
But now at leas...