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Thought I had a bad battery but now car won't jump, help!

So, I bought an old used car about two weeks ago. I was told that the car had been sitting for awhile and the battery wasnt really holding a charge. It started and ran fine the first couple of days then i would find that the battery was dead and needed to be jumped to start. after a couple of days with this happening every now and then, it got to the point where in order to start the car it had to be jumped. I did this for a week and this morning when leaving i jumped the car, drove about a mile before the car just died as I was pulling into an intersection. I should mention this happened once before about 4 days ago but the car was able to be jumped. This time however the car won’t jumpstart. It sounds like its trying but it wont turnover. I was thinking alternator… any ideas? by the way its a 1990 plymouth acclaim.

Sounds like you need a new battery…doesn’t seem like the battery is holding a charge.

The lights and all were coming on when i attempted to jump it, could this still be the battery?

You knew the battery was bad when you bought the car. Now the alternator may be damaged from trying to keep the dead battery charged.

I suggest having both the battery and the alternator tested. Most parts stores will do it free.

You can’t keep jump starting a car every day. The alternator isn’t designed to charge a dead battery. It’s only meant to maintain a charge on a good battery.

Yes. The lights only need 12 volts, maybe less. The starter needs lots of amperage, which your battery no longer has.

Modern cars are started by the battery, then run off the alternator once started. The battery is recharged by the alternator. If the alternator is bad, the car runs off the battery and doesn’t get charged. Eventually, the battery will run down.

If you have been jumping the car to get it started, the battery was supplying some of the required amperage to turn the engine over. Without being recharged, the battery got weaker and weaker until now it doesn’t have enough power to assist the jump start. Even if it were to start it wouldn’t run very long.

The alternator is bad and needs to be replaced. Since you’ve run the battery to a deep cycle (dead) it may or may not be able to hold a charge, but it should be put on a battery charger and then the cells tested to see how strong they are.

Ideally, replace the alternator and the battery (or have the battery charged and tested).
If money is a problem, if the battery is still good and can be recharged by a friend you can manage to drive it during daylight hours. Running the headlights will seriously drain the battery and ultimately all the draining and recharging will kill it and you will need to replace it (and the alternator).

The biggest drain on a modern fuel-injected car is the fuel pump. You used to be able to run a car a long way without the headlights , but no more.

So, an update now. I bought a new battery and put it in the car, it started up fine, i drove it home. I self tested the alternator and it was running fine. I left for work this morning, drove about 6 or 7 miles and as i was getting on the onramp to the highway, the steering wheel started to vibrate as the engine tried not to cut off, but the car did indeed cut off. i couldnt restart it immediately but after it sat for about 15 minutes i was then able to start the car. I drove straight to the nearest advance auto about 3 miles away where they tested the alternator battery and starter. everything came up good. i drove the car home, not wanting to test my luck further. I’m thinking that there’s something causeing the car to knock off while driving and now that i replaced the bad battery i’m able to restart the car without jumping it later. my question is what’s causing the car to knock off? any ideas?