In-line Isolator is perfect for my need!

I just figured out lately that the 3Amps fuse of the power supply I used to charge my isolated 28AH battery is always being destroyed each time I use it. It took sometime for me to figure out what's causing this frequent breakdown.

What I found out is that at the beginning, the battery is very weak so it is only capable of sending out less than 3Amps. When its terminals are connected to a load(my 12V 3Amps power supply), the battery acts as a load instead to the power supply since the power supply can send 3Amps max. On certain occasions but lately, it is more frequent, that whenever I connect the battery to the power supply, the battery is adequately charged but not to its maximum level but it can be capable to send out more than 3Amps. That is the time when the 3Amps fuse which acts as a circuit protector gets busted.

So I have identified the problem, what I needed is an electronic device that will totally isolate my power supply from the battery and that even if the battery is adequately charged should not prevent my power supply from doing what I wanted it to do and that is to continiously charge the battery. So for now, I am searching the web for an in-line isolator, preferrablly should have the following features:

1. Prevent my 3Amps fuse from getting busted 
2. Should allow my 12V 3Amps power supply to continiously charge my battery.
3. Should be capable to handle at least 36Amps or more since my 28AH battery  is still somehow connected to my main battery bank which is at 72AH already
4. It should be a full product not in the form of electronic widgets.

I would really so be very happy if in the next few days I would be able to find a product like this locally. I know that such a gadget will be difficult to find.