1. The new laptop batteries are not fully pre charged, you have to charge them in your laptop before you expect some or full backup from a new battery.
2. When a laptop is not working, some buyers assume that the battery replacement is required. Please be aware that the laptop works well directly through ac adaptor even if the battery is not installed. If this is not the case, please do not directly buy the battery unless your laptop works well with ac adaptor.
3. If your old battery is totally dead ie if the laptop gives zero backup with your old battery then, there may be two possibilities :
(a)The old battery is dead and laptop is ok. In this case, only replacing the battery with new one, will solve the problem. For this, just install the new battery into laptop and allow 3-4 hours to get it fully charged. During this time, you may keep working on your laptop.
(b) Old battery is dead and the battery charging circuit inside laptop motherboard, is also dead. In this case, the new battery can be utilised only after you get the laptop motherboard repaired from any expert technician.
If you have any similar laptop battery near you for checking, you may try using that battery to check if laptop charging circuit is able to charge any battery and if that battery gives some backup time even if it is 4-5 minutes.
Please be informed that laptop batterries should not be allowed to remain fully discharged for long time. If allowed, they becomes dead and unusable.
I hope the information given above, will help you reach proper buying decision.