Battery replacement on 520T

Can the battery simply be replaced with 1.2 or 7 or even 35Ah? In other words, can the module that comes with 520T handle more amp/hr battery? If so, do I need to change the fuse to higher amp rating? Autotoy appears to be the one and only store that sells 7Ah battery WITH charging/wiring modules. If the battery of 520T is replaceable with any type that'd save me money from getting a 7Ah from autotoy. I have seen some 35Ah for a good low price. Unlike what most car stereo people would do, I ONLY want to use this battery to power my alarm and the accessories (train horn/air horn/underground light/siren) when the main battery cable gets cut off. If the battery of 520T is NOT replaceable with any type, does the following work? *85 -> (+) igniton switch 12v *86 -> (-) chassis ground *30 -> (+) positive post of backup battery *87 -> (+) positive post of main battery (diode needed here?) *87a -> (+) positive post of main battery but with a cut off switch *negative post of backup battery to good chassis ground *alarm brain and all accessories mentioned above connect to positive post of backup battery

The unit should be able to handle nearly any sealed battery you can find, so long as you aren't trying to charge a bank of deep cycle batteries with it.time is bending.....

Do I need to replace the 18 gauge (to constant +12V) wire and the 15amp fuse to something so it can handle the higher load or the higher Ah is irrelevant? Or just leave them as is and just let the battery module to do its own job like giving it much more time to charge a 18Ah than 0.7Ah?