My battery charges but when I use it for an couple

Could be a bad battery. Check it with a different battery

Try another charger, yours may be faulty. Alternatively,the battery may need replacing as it is no longer holding charge, these can be obtained very inexpensively from Ebay and you will just need a small cross head screwdriver to remove the cover on the back of the DS lite, then tap the unit in your hand to dislodge and remove the battery.

it sounds like it's a battery problem.

If you want to replace your battery, call Nintendo's Consumer Assistance Hotline at 1-800-255-3700 from 6 a.m. to 7 a.m. Pacific Time, and order a replacement battery there. I believe it costs around US$15.00.
If you still need assistance I would suggest you check our online troubleshooting here. Depending on the specifics of your situation, the problem may be the DS Lite, the battery, or the AC adapter.
PCHELPSTER007 from youtube
p.s. Before doing this you could maybe try using a different charger

Could be.Those batteries leak charge even when not in use.I would let it go for 24-48 hours just to be sure.Unless the batteries or charger becomes very hot.

This is OK the Red LED Has just gone out... simply just keep an eye on time if you think that it might die soon plug it in... there is not much that you can do to fix it.

The red LED indicates low power. When the DS is charging an orange LED should be on and the DS can be switched on, giving a second green light. If you tried charging it but the orange LED did not come on or only came on for a few seconds then the battery has not charged. The charger may be faulty or the power connector on the DS may be faulty. You need to try another charger. If another charger does not work then the DS is faulty and needs repair. It could be the power connector or the battery or some other fault inside.
If the amber LED comes on to indicate that the battery is charging then the battery should be fully charged within 3 hours. If the DS does not switch on after charging then the battery may be faulty. It can be removed by opening the cover on the bottom of the DS.
You should try and find a friend with a DS who will let you try their charger and battery in your DS.
If the DS itself is faulty it will probably be uneconomical to repair. If this is the case then try selling it on ebay as a faulty DS.

Sounds like the battery is completely drained. Remove and replace battery, and charge for a couple of hours with your AC charger. If it still does not fully charge, you may have a bad battery. Good Luck...

Here is the manual:
http://toolboyworld.com/eBay/Ryobi_P120/P120_566_eng.pdf

Red = quick charge
yellow = evaluating
green = charged

CHARGING A COOL BATTERY PACK
If battery pack is within normal temperature range, the red LED on charger will come on.

Red LED should remain on for approximately 1 hour then the green LED will come on. Green LED on indicates battery pack is fully charged and charger is in maintenance charge mode.

I don't know how to solve your problem but, the three lights mean this:
Red LED light indicates the battery is being charged
Green LED light indicates that the battery is fully charged
Amber LED light incidates that the battery power level is low - the battery needs recharge.
Do not recharge you battery over 24 hours.

Hello,
Here's a copy from the owners manual:
■ Charging LED 
Red LED is on = Being charged 
Red LED is blinking = Charging error 
Green LED is on = Carging is complete


● If the charge indicator blinks as red, it indicates a battery charging error.
- The battery is not properly inserted
- The terminals of battery are dirty or damaged
If the battery is inserted properly and the charge indicator continues to blink, contact the
nearest Samsung Camera Service Center.


Another charging error is when the batteries are so depleted, they won't charge up to 100% anymore = red light doesn't go out and remains on for too long, means get a new battery.