|No video doesn't necessarily indicate you have a battery problem.|
Either of, or both of , battery and/or charging system problems, and problems with the built in display, can cause no video.
You haven't supplied enough symptom information for us to determine which is more likely.
E.g. when you have no video
- do the leds light up like they normally do ?
- do you hear that the hard drive is spinning ?
- do you hear the fan spinning ? (it often comes on when you are booting but then stops spinning and comes on after that only when it's needed.)
"has been no physical trauma to the machine."
Are you SURE ?
Have you, or is it possible someone else who had access to this computer...
- dropped it, or dropped anything on it, or otherwise exposed it to a physical jolt ?
- spilled liquid on it, or sprayed it with liquid, or exposed it to liquid such as rain ?
Has there been a power failure event that happened recently while the AC adapter was plugged in ?
"last time i just took out the battery and rebooted on ac power, screen came on, but that is not working this time,"
If it worked before it should still work. You probably have a problem with the AC adapter's cord or the plug on the cord or with the jack it plugs into in the laptop.
"tried with only batter power, works with secondary moniter hooked up "
If the computer and it's video works fine with the secondary monitor with only the battery hooked up, you probably have a problem with your built in display, NOT the battery.
If you are having problems with the AC adapter's cord or the plug on the cord or with the jack it plugs into in the laptop, you are probably having intermittent problems with the battery being charged properly.
Laptop no video (or video problems), and battery, AC adapter, power jack T shooting.
See response 1:
DO NOT plug in or unplug a monitor's video cable into / from a video port while the computer is running. Doing so can damage the monitor's circuits and/or the video adapter's circuits.
Some laptops will display on an external monitor without you having to do anything.
If you get no video on an external monitor, some laptops have a key combo that you must press to toggle the display to external video only / built in display video only / sometimes both - see the Owner's or User's manual for the model.
If there is nothing wrong with your AC adapter or it's connection and the jack in the laptop.......
Laptop main batteries usually work as they should for a year or so, then they begin to rapidly deteriorate. From what I've seen, by two years they cannot be charged to anywhere near their full capacity, and it gets worse after that.
They often develop internal shorts when they are older. If the battery gets HOT rather than just warm after you have attempted to charge it for at least a half hour, or after you have been using the laptop for a while with the AC adapter plugged in, it's definitely internally shorted and you must replace it. Internally shorted batteries getting too hot have been known to cause the laptop to catch on fire.
Tips about battery charging problems on Dell laptops - may apply to other makes.
See response 3 in this by iTech: