NEO GEO

I just had one of my batteries go completly dead and it was like that for a 2 or 3 weeks or so till i found out. what i like to know did anyone in this forum ever use the battery additive that is suppose to bring the battery back to life? I do know that when a battery goes dead (for weeks) without charging it they never come back to take a charge. so can anyone here that had this problem ever try these products, and what product if any do they suggest? Thanks for any help NEO GEO