[Lil bastard]

Sounds as if the battery may be at fault. If the battery has been run down in the past a few times (perhaps prior to your acquiring it, and therefore unknown), it's future ability to accept and hold a charge is seriously impaired. And further so with each successive discharge - the effect is cumulative. Also, any battery 4 yrs. old or older has left it's best years behind it. Your '05 could have been produced and sold as early as 8/04, so (assuming it's the original) it's coming up on that benchmark.

Could also be damaged. This happens more often than people think. Hit a pothole or good bump and it's possible to break the fairly fragile lead plates, or crack the case between cells.

Then too, it may have a low or diluted electrolyte level.

Check the battery with a multimeter (battery cables disconnected). It should read no more than 13 volts, ideally about 12.6 (batteries usually contain 6 cells, each producing approx. 2.1 volts). If this is not the range the multimeter indicates, then suspect the battery, especially after already having it on the charger. If the voltage is below this level, suspect loss of electrolyte, sulphating, or damaged plates. If above, suspect cracked case between cells which are shorting internally.

Finally, with the battery connected, car running, all electrics turned ON , incl. High Beams (called a Load Test), check the battery again with the multimeter. This time, it should read between 13.8 - 14.2 Volts - this is the voltage supplied by the alternator. If not, you may have a faulty alternator, most likely the diodes. If below this range, the alternator likely caused the plates in the battery to sulphate. If above, the alternator may have 'cooked' the battery, causing it to boil off it's electrolyte.

If that's the case, you'll need to replace or rebuild the alternator in addition to replacing the battery. Good Luck!