upgrading the dei 520t battery backup

I know I have seen a post on here where someone added a resistor to the 520T circuit board and a much larger 5ah battery. My question is, do you actually need to do this board level work, or can I just replace the battery with a larger rechargeable one? The little 0.7ah battery that came with the 520T would not go for long powering the 2 sirens, iDATALINK, glass break sensors & brain very long at all, so I am looking into what my alternatives are for having a larger rechargeable battery.

You can just add in the bigger battery, after all, it is the same operating voltage!commit your way to jehovah and he will act in your behalf. psalms 37:5