So it's the beginning of the mowing season for us and I put my X300 on the charger for awhile. It still didn't have much battery voltage so I jumped it with a regular 12 volt car battery in my Cub Cadet compact tractor. The JD initially started right up and then quit, now nothing! I checked the fuses on the firewall and the 15 amp fuse was blown. I replaced the fuse but still no start, no clicking, nothing. My Owners Manual says it could be a fusible link. Where is the fusible link on an X300 and what does it look like? Would my slightly larger 12 volt tractor have blown a fuse? Yes it was hooked up correctly. I went to a John Deere parts site but couldn't find any reference to a fusible link and my manual says to check with the dealer. Surely I don't need the dealer to replace the fusible link?
To answer the question about the larger battery... yes it will blow fuses and fusible links because the Amperage is too much for the circuits on the rider. Voltage is just the basic power potential; the real power comes from the Amperage a battery has stored. The compact tractor was likely a 600 Ah battery while the rider was around a 300 Ah battery.
When you check the fuse link wires, tug on them to see if the insulation stretches, that will indicate it is broken, they do not always burn through the insulation because it is heat resistant.
Fusible link wire can be purchased at most parts stores, but you have to know what gauge. Typically, if your main power wires that have fusible links in them at the starter are 10-12 ga. then a 14-16 ga fusible link would be sufficient. The larger starter cable does not have a fusible link. (Note: The higher the gauge of the wire the small diameter of the total strands it will have.)
A fusible link is a safety device like a fuse, but it can temporarily handle high Amp loads for a brief period whereas a fuse would immediately pop the center element open.
Whatever you decide to install, it needs to be soldered and shrink taped at the connections. Quick butt connectors will create problems in a short time due to moisture and dirt exposure.