If you have been using older NiCad batteries your charger wont handle Lithium cells go for NiMh types.
Make sure they are fast charge types and a good capacity 3Ah is best.
As for the batteries in general 90% of them are made in China nowadays, even reputable drill manufacturers have quality control problems from time to time.
Look them up on ebay you will probably find replacement packs for a reasonable price, just double check the specifications.
If you have had your drill for 12 years I can only assume you have not used it very heavily but consistantly otherwise your batteries would have packed up a long time ago.So a top line drill is not probably needed Go for middle range ones similiar to Ryobi.