Latitude C640 Won't Boot from Good Battery

I bought a refurbished laptop from a distributor on ebay, who I discovered doesn't know the true meaning of refurbished. But to make the long story short, after I installed a new CMOS battery, and purchased 2 new laptop batteries because the dead CMOS killed 2 other batteries, I now discovered the laptop will not boot up using just battery power with a full 100% charge.

When I press the power button, the battery LED's light up like it was charging the battery. It's 3 green 1 amber, and it dos this about 4 times before stopping. None of the lock lights, light up (just threw that in there in case it is relevent).

I can boot using A/C power, and I can disconnect the A/C power and the battery will keep the laptop working, but it won't boot using just the battery. I'm not sure if this means anything, but when I disconnect the A/C power, the screen dims at least 10%-20%. Is this typical of an older laptop; to have a dimmer screen when using battery power?

In my laymen's opinion, I feel there's probably something wrong with the internal voltage regular or something, but I hope I'm wrong. I really like this laptop but in hindsight, after all the time I spent "refurbishing" this laptop; after needing to buy 2 laptop batteries, a new CMOS battery, and downloading an English spell check for Outlook because I don't speak French, I should've just spent the extra $200 and bouight a brand new Acer or something.

Thanks in advance for your answers and time.

Frank

I just realized that I can "restart" the laptop using just battery power without any problem. I ran the diagnostic by pressing F-12 key. All tests "passed" but at the end of the test, a dialog box appeared and stated "No Diagnostic Utility Partition found," enter the Drivers and Utilities CD. Unfortunately, I didn't receive this disk.

I meant to say that I "cannot" start the laptop using just battery power, but I think you're right - it must be a MOBO issue (see below). Odd enough, there aren't any thorough explainations for LED battery code sequences anywhere to be found. There's plenty about the Lock Lights, but not battery LED's - even in the Dell C640 manual itself.

All along, I was getting 3-greens and 1-amber/orange while the battery was charging, and it was charging up okay. But for some odd reason yesterday, and only when the laptop was on, the battery began re-charging and instead of getting 3-greens followed by 1-amber light, the LED remained solid green until it took a full charge (or at least to 99%). Then it blinked green only, slowly on & off, indicating the charge is done (assuming that's what this means).

However, this morning, it still wouldn't boot up from just the battery so I decided to remove the CD drive from the modular bay, and place the battery in it. Fortunately, that fixed the problem and it will now power up from the battery -- but only when the battery is in the CD bay (one problem solved, another problem created).

hence why I agree it must be a MOBO proboem, or I need to get into a setting somewhere.

In the BIOS settings, and in the part of the BIOS I cannot change except for the date & time, I see it states Modular Bay: BATTERY at the bottom. Is there a way to change that from Modular Bay: BATTERY to perhaps Modular Bay: CD ROM or something else.

Frank