Do these waveforms look appropriate for charging an 11.4 V, 3830 mAh lithium ion battery?
The chaotic, noisy, huge voltage signal (±150V from a 15V input??) is a sign that your simulation has gone off the rails, and that its results cannot be trusted.

As a first step, add a ground to the battery side of the circuit. Yes, I know it isn't actually grounded… but leaving that part of the circuit floating is likely to confuse the simulator.

If that doesn't help, try decreasing the time step.