From what you describe and assuming the new battery was "new", I'd say you have an internal short which is draining the battery over a short period of time. I'd also investigate the accuracy of the battery charge indicator. Download this free utility which will give you a more accurate picture of your battery:http://www.mioplanet.com/products/batterymeter/
I'm assuming you gave the battery a "commissioning charge" when you bought and used it?
If not, this is something you should do with all new LI batteries. This bit is reproduced from a website that sells batteries for the Toshiba satellite series:"2. The new Toshiba Satellite a205-s4777 battery pack needs to be circled
(fully discharged and recharged) three to five times to reach its
3. Toshiba Satellite a205-s4777 battery will undergo
self-discharging when left unused for a long period of time. Thus, it
should always be stored in a fully charged state and kept in a cool, dry
and clean place.
4. It is normal if the new Toshiba Satellite a205-s4777 battery
gets warm when being charged or used. However, please pay special
attention if the battery pack becomes excessively hot. This may indicate
there is a problem with the charging circuit of the electronic device.
Please consult a qualified technician if necessary.
5. To maintain the optimum performance of Toshiba Satellite a205-s4777 battery pack, it is highly recommended to circle (fully discharging and recharging) it at least once a month.
6. New batteries are hard to be charged. Sometimes, your
electronic device may indicate a fully charged condition about 10 to 15
minutes when Toshiba Satellite a205-s4777 battery pack is being charged
for the first time. When this happens, remove the battery pack and let
it cool down for about 10 to 15 minutes then repeat the charging
procedure. Sometimes, the new Satellite a205-s4777 battery will
suddenly refuse to be charged. If this happens, a suggested solution is
trying to remove the battery from the device and insert it again.