Bike needed to get jump stated & runs really rough. stalls when i apply brakes & tach goes nuts. bad battery?

basically i know battery needs replacing. today i went out for about 100 miles with no problems each time i stopped. then last time i went to start, the lights were dim & only clicked. i jumped it like many times before & bike ran really rough & sputtered all the way home. i had to keep it in 2nd and keep on the clutch. the headlight would get bright then dim. the tachometer was all over the place and each time i would apply the brakes the bike would stall and im back to square on with having to jump it. could it be that the battery is so far gone its messing with the electrical system? possible alternator? i did leave a gps accidently plugged in for a few hours which could have drawn down the battery? this is by the way a 2001 kawasaki ninja 250cc.

Yeah that's what my older brother's bike did and it turned out to be the battery. Try getting it replaced ASAP. After that, its lasted about 7 months now with no problems.

Hope this helps and hope you give me best answer :)

You said you jump started your bike. Was the car running? That is a no no. If you jump off a bike just connect the battery from the car to the battery on the bike and start the bike. This could have blown out your regulator rectifier and/or stator. Bikes use a different system thus do not have alternators.
Regardless if the car was running or not....sounds like rectifier and/or stator. I saw a used stator for your bike on eBay for $40---rectifier was on there for about $20. Start with the rectifier.

I have a 81 Kawasaki that was doing the same thing. The IC Igniter was bad and the ignition switch was shorting out. I replace both and installed a new Battery and spark plugs. The bike runs like a new one now.

If you have a motorcycle junk yard close to you that the owner doesn't think all his junk is new then You should get the igniter for around $100.00. The ignition switch for about $50.00

Possible alternator or regulator, battery going lower because of weak charging system. Time for a voltmeter/amp-meter check of alternator and battery charge check. could check brake wires- almost sounds like a rubbed brake light wire involved also. Battery ground cable check also- corroded ends with poor ground can cause varying voltage symptoms.

i would believe it has something to do with the charging system and maybe one of the wires is shorting out

i had a simular problem and it turned out to be the spark plug was loose..