If the new one will fit in the case you can use it. If the new one is one of the more exotic chemistry cells then you will want to use the appropriate charger. The simple wall wart style charger can only be used with nickel cadmium or nickel metal hydride.
Anything with lithium as part of the chemical system needs to use a fancy charger to allow proper charging without damage to the pack.
Assuming that this is a Nimh pack and again assuming that you want to use the old wall wart charger that came with the set keep in mind that it was set up to charge up a 600mah pack overnight. So the charge rate will be too low to charge a 2500mah pack to full charge in that same amount of time. Instead you'll want to leave the charger connected for a good 48 hours at a time to ensure you get up to somewhere close to a full charge.
Last edited by BMatthews; 03-02-2014 at 09:34 AM.