Presume the laptop continues to work ok when the power supply connection is plugged into the mains electric and your are noticing that the battery is losing its charge capacity?
If so, sounds like the battery is in need of replacement, especially if it has been in use for some time with lots of discharge / recharge cycles.
Depending on your exact Toshiba model / battery number type you should be able to purchase a battery replacement via searching around on ebay, for example:-
http://www.ebay.co.uk/sch/i.html?_from=R40&_trksid=p2050601.m570.l2632.R2.TR10.TRC1.A0.H0.Xtoshiba+laptop+batter.TRS0&_nkw=toshiba+laptop+battery&_sacat=31530