Hi and welcome to Ninjette!
What year is your 250?
You should slow down and do one thing at a time and do it correctly. Otherwise you may be replacing a lot of blown up parts.
1. Remove battery from bike and put on trickle charger for 2-3 days. Check acid level and top off with distilled water as necessary. In meantime...
2. Make coloured decals for battery terminals and battery cables. Make + red and - black. Or
buy them from here. Apply to battery and battery cables
3. Pull
every fuse and measure resistance across legs of each one. Post results here. Such as:
main fuse = ??? Ohms
fuse #1 = ??? Ohms
fuse #2 = ??? Ohms
etc...
4. With key ON + kill-switch ON, measure resistance between each RED terminal at each coil and +battery cable
5. Drain all petrol from tank and carbs. Replace with fresh petrol.
6. After couple days, measure voltage of battery and post here
With all of his data gathered, we can then come up with step-by-step plan to get your bike running. Might require thorough carb refurb, and possibly replacing CDI box, coils, switches and/or entire harness (depending upon how much was melted).