charging issues

I have a 1982 Suzuki GS750T and the battery is not staying charged. I got it started and disconnected the ground from the battery and the bike died immediately. Does this mean that my battery is bad or is there something else wrong?

Thanks!
-Tyson

Is the battery a new one?

If not, it could be a natural death.... got to buy a new one.

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Motorcycles have permanent magnet field excited alternator stator type charging systems. There are 4 distinct and separate parts to a typical motorcycle charging system: Battery, Stator assembly, Permanent magnet exciter ring, Rectifier/Regulator assembly. Each has a separate test, but you can backyard the following tests I will describe. But first you need to know that motorcycle charging systems are usually low amperage systems that also do not charge well at low rpm (idle). They are not big amp systems like what 4 wheelers use. Because they are small systems, little things can and usually do affect the battery life of the bike.
A common miss on electrical diagnostics is to ignore connections and grounds. Before you start condemning anything, clean every connection you can find that is related to the main and charging circuits including the battery positive and ground wires at both the battery and where the wires connect to the bike. This is very important! Cleaning connections and insuring minimal resistance in the wiring is cheap, especially when you are faced with spending big bucks replacing charging system parts.
To test what is wrong (battery or bike) First recharge your battery and then connect a voltmeter to the positive and negative terminals (battery installed in bike). Your battery voltage, at rest, should be at least 12.6volts. If the battery voltage is below that, first try slow charging the battery for an hour (never allowing the charge voltage to exceed 14.5volts) and recheck. If the battery continues to be below 12.6 volts, you might have a bad battery. Once you are sure that the battery you are using is fully charged, note the battery voltage at rest. Now turn on the key, head lamp and marker lites. Note the voltage. It should have dropped about .5volts to a max of 1volt on a marginal battery (size or condition). Leave key and stuff on for 1 minute then turn everything off. Note the battery voltage again. It should regain 80% of its original voltage at rest as noted before the test. If the battery falls below 9.6volts at any time of this test, the battery is bad (usually sulfated). Note that sulfated batteries can recharge to 12.6volts but have no reserve power for cranking etc.
Now start the bike and note the voltage at idle. If the charging system is helping at all, it will show slightly better than the voltage you saw when doing a Key on / engine off test. Now rev the engine up to about 2000 rpm and again note the voltage. It should now be climbing over the voltage of the battery at rest. The voltage of the bike should eventually settle around 14 to 14.5volts when the battery is fully charged and the alternating system is supplying an abundance of amperage.
If at any time the voltage climbs above 15volts, shut down and suspect a bad regulator. Out of control charging systems, that overcharge batteries, not only damage batteries but also blow lightbulbs and worse, can damage bike electronics!
If you remember the above, you can maintain, check and test your battery, charging system at any time, thus saving you tons of "I gotta feeling its ..." mistakes.
And finally NEVER DISCONNECT YOUR BATTERY WITH YOUR ENGINE RUNNING! Nearly certain damage to your charging components will occur. The battery is vital to the stability of the electrical system, it's removal will cause often fatal (to equipment) voltage spikes that attack electronics as well as electrics.