One or two more points:
since it hasn't been started for a while,
1) you might check also on the scoots RH side above the cooling fan grill:
-there are two cables coming out from the engine block, covered by a black rubber grummet.
This two cables should (during starting mode with jump vables) around 40 VAC.
- if NOT, the likelyhood of a rotten/broken alternator coil is high.
2) go with a multimeter on both PLUS and MINUS which lead TOWARDS your battery
-watch MM
-good battery
-start button
- now your MM should show at least 13.8 to 14.2 VDC.
If NOT, one of your pieces in your chain (alternator, cables, connectors, rectifier/regolator) is faulty.