Why is battery not working?

The check engine light could relate to something else - not your battery or alternator.

If your battery isn't charging from the alternator an illuminated battery symbol would appear.

It could be many things - low oil level, low coolant level, low windscreen washer fluid level. It could even be an electronic 'fault' - which a computerised diagnostic check would identify.

If the battery warning light is illuminated the first thing you should do is to check the tension of the alternator belt. You say that a new battery and alternator have been fitted? Take it to an auto electrician - he should identify any fault within minutes.

Dear Joyce,
The "battery not charging" light actually will tell you many things, and that one light is affected by several parts of the car.
If your battery is new, then the light is telling you some other part of the charging system is failing or has failed.
The most common part is the alternator.
The alternator, or the voltage regulator which is built inside the alternator, can both fail, and the light is telling you.
Those need to be checked by a repair man. (mechanic)
If you have no corrosion on the battery terminal, or the wires, or inside the insulation of the wires, the alternator should be your problem.
God bless your efforts.

Test the alternator. The battery light is for the charging system. Once the charging system is working with the engine running, the light should go off. If your light stays on with engine running, the alternator may need service or replacement.

To test the charging system, just put a voltmeter on the battery with engine running. The voltmeter should register at least 13.5 volts- alternator is charging. If you only show battery voltage with engine running, like 12.2-12.8 volts, the alternator or charging system is not working. The battery light should be on to signify this.

your alternator is still under warranty get a new one, based on your info thats the problem, just make sure when installing the new one the battery polarity is correct because that is one cause of damaging the alternator, reversed polarity will burn regulator ic, once you have installed the new alternator run the engine on idle remove one of the battery connector if the engine still run it means the alternator is charging, if engine stops check wiring connection

Its probably the alternator.
The warning light comes on anytime alternator output drops below 12 volts.
I should also tell you, you can't check an alternator by running the engine with the battery disconnected. The alternator needs the battery in series for the diodes to work. What you did could have damaged the alternator and also the engine computer. Only generators can be checked by disconnecting the battery.

Have the charging system checked. Maybe the new alternator isn't charging. Is your battery light on when running? If you put a voltmeter across the battery terminals when engine is running, you will know if alternator is working or not. You first should have the battery charged up. Voltage should read at least 13.5 volts, engine idling. If you just get battery voltage, say 12.6 volts, alternator is not working:. Check all battery and alternator connections for a clean, tight connection. Battery cables and connections should be inspected. Check for any blown fuses, your truck may have fusible links- if any are bad, you need to replace them. They would be located close to the battery, as they serve as power distributors.
Good luck.

well if the battery light came on that means your alternator is not charging the battery,,you need a new alternator,,,and maybe a new battery if it killed it,,,,that set the check engine light on,,,,,for it not charging,,,,,do not buy a aftermarket alt,,,,only saturn/gm,,as they do not meet gm/saturn specs and you will install it and still have a battery light on,,,,,,you need a factory alternator,,,yes it costs more,but unless you feel like putting a few in and out to find this out,,,,,

Check the 'Bat' / 'Charge'/ 'Alt' indicator on the dash panel lights when the vehicle ignition is switched on prior to starting the engine.
This indicator should extinguish within approx 1 second of starting engine.

If the indicator is not operating the alternator cannot provide charge current - check:-
1) the wiring connections to the new alternator,
2) the indicator lamp is not blown,
3) the alternator is properly grounded.

If the indicator light works normally, check the output voltage of the alternator is approx 14.5v when the motor is running.
If its about 14.5v, the battery should be charging.

Is the check engine light on? If so take it to a local parts shop like Advanced Auto call ahead to see if they have the machine to check the code, if the check engine light is not on then I would say that it is in fact the alternator.

Well i would take it to a shop and have them check the alternator when its in the van running under load.