Do I need a new battery

I went on vacation for 4 weeks and came back to a completely dead car. I tried one of those battery cahrgers that plug into the cigarette lighter....didn't work. I got a jump start and everything was okay for about a week. Now, it's starting up very slugglish, even within only a couple of hours of it running for at least 30 minutes. Did leaving it for 4 weeks kill my battery? Could it be something more serious?

Ok, think about this for a minute. Where does the cigarette lighter get its power from? The battery. If you try to charge the battery with the cig lighter, you're trying to charge the dead battery with.....itself.

You need to connect jumper cables to it for about 2 mins with the other car running. Try to turn it over. Once it starts, let it run for a good 10 minutes with no accessories or anything. Take it on a nice little drive with no a/c / heater or radio, for like an hour or two straight, preferably not in town. If you still have problems with it, just get a new battery, they aren't that expensive.

Also, keep in mind, the car recharges itself while you drive. The more time you have the engine on compared to number of starts, the better

Hey Alee.
I currently work in renewable energy (power inverters) and can give you a few rules with lead acid cells:

Cold batteries leads to accelerated self-discharge. (E.g., You may have heard never to store a battery on concrete floor.)

Flat batteries have much lower pH (stronger acid), which rapidly chews out the lead plates.
Thus: Flat battery x time = dead battery (poor capacity).

3 years is about the limit of expected life for most lead acid's. But 4 weeks away without topping up will usually bring a "halfway" battery to it's demise.

If you drive for an hour (lights off) and it's not back to normal, DEFINITELY time for a new battery.