What MOSFETs are you using now, and what MOSFETs were you using before?

I didn't think to ask if you were using the exact same MOSFETs in the real circuit that you showed in the simulation.

 

Hi there SgtWookie,

I tried replacing the p-ch mosfets with n-ch mosfets today and I didn't get any substantial result. The n-ch mosfets start conducting without the charger connected, unless I dont connect Q10. If I do that then there would be no way the battery charger will start.

I think I am going back to my original design, p-ch mosfets in source follower configuration connected to a single n-ch mosfet inform a push pull arrangement. In theory, this should work but I just don't know why it isn't.

The p-ch mosfet: IRF9540, n-ch IRF540.

I will provide more information as I get them.

 

I have seen some complex models for lead-acid batteries. Have you Googled "lead-acid battery equivalent circuit modeling"?
I have used a large capacitor (farads) in series with a resistor (milliohms) and a high-value parallel resistor (for leakage or load) to test battery charger simulations. They worked well for me, but I never actually built the chargers and tested them.