After almost a week of hunting, I did not find an existing electronic gadget that I called in-line isolator but I got an alternative solution. I've searched everywhere, almost all electronics stores, online shops and even the wikis, I am so surprised it does not exist.
My solution is quite simple and straight forward but I still need to upgrade it in the future. What I did was, I bought 10 pcs of rectifier diodes which are rated at 6Amps/500Volts and connected them in parallel. The basic idea here, is that all 10 diodes have equal resistance(if any) and therefore the current that will flow in them will be equal, and at the same time having them connected in parallel would mean they can be a lot stronger to withstand any electrical sparks. I am now using it and it is doing its job flawlessly.
The only problem I encounter is that the power supply has lower output voltage than the battery, so as a result, it will only be effective if its output is boosted up to 14 volts so that it can charge the battery. I feound electronic widgets that will solve this problem and I am still waiting for them to arrive because I imported them from China via ebay.