Replace battery with new one, show charging, charging complete, unplug, battery is dead

Please describe what "Completely went dead" means.

Did it fully Power Off?
Did you have to hold the Power button down for a while to get the phone to go through a Restart?
Did the phone come back on when you pressed the Side button?
A little more detail, please

Hello,I would get back to where you purchased the batteries and go from there.Take the charger also to ask them to test it,also keep the old batteries as they are as you say.Still okay.Take care and I hope this helped you.Colin

Remove battery, check if the phone works just with charger. If the battery is in 0, the phone doesn`t necessary understand it...

The fact the battery is 3 months old means zip, I have replaced dozens of batteries under warranty, many less than 3 months old. have it tested with a load tester.

Three possibilities;
1) You have a dead battery because the battery is no good.
2) You have a dead battery because your Sansa is no longer charging the battery.
3) You have a dead battery because you didn't leave your Sansa tethered long enough to charge it up.

When you have the Sansa c250 tethered to the computer, you should see a tiny yellow lightning bolt flashing, and a battery icon that shows the amount of charge on the battery.

If you see the lightning bolt, but the battery does not charge after being tethered to a working computer or charger for 24 hours, you may need a new battery. You can get one on Amazon.com. Here's a link:
http://www.amazon.com/HQRP-Replacement-Battery-Universal-Protector/dp/B001NZ981S

If you see the lightning bolt, and the battery charges after 24 hours, AND your player works when unplugged--Problem solved! You just need to let it charge for a longer time.

If you do not see the lightning bolt when the player is tethered, and the battery indicator shows "empty," It's likely that the internal plug to your Sansa c250 has broken. Your Sansa is no longer able to charge the battery.

If you happen to be an electrical engineer, or otherwise have a shop full of electronics equipment (including signal injector, volt-ohm meter, needle-tip soldering iron, and stereo magnifying goggles with work lamps) you may be able to fix it yourself. Otherwise, forget it-- your Sansa is dead.

If it's still under warranty, try to get it replaced. Failing that, it's time to get a new MP3 player.

Hope that helps! Please post a message to let others know what happened to your Sansa player.

bad battery
bad ac power pack ( weak not dead)
bad battery charger chip on the main motherboard.

Sorry. It seems that your battery is dead.
If your laptop is working fine on AC power only (with the battery disconnected), then your battery will need to be replaced.

you can change battery and/or upgrade hard drive (if changing hard drive, save the software to pc then copy to new hard drive)
how to replace battery / hard drive
check and follow this link http://www.youtube.com/watch?v=6HOnpHSgMvw

if you dont have tools http://www.ipods99.com/Default.asp?Redirected=Y

bad battery.. RMA that back to where you bought it from. probably wasnt a new battery they sold you. id charge it from completely dead to completely full one more time and if you dont get at least an hour out of the batt then i would return it..