Buy from a trusted retailer that warranties the battery. Parts-People is a reliable supplier of genuine Dell parts and they have batteries for your laptop in stock. You can also buy direct from Dell.  If you buy elsewhere, be careful because there are many counterfeit batteries sold. Ask the seller about warranty and ask about production date/age of the battery.  
Hello, I own a Dell G7 7790 laptop bought in 2020, recently I did all the battery tests with SupportAssist app, on Dell website and in BIOS as well and the result was that I had to change it.I have received an original Dell Alienware G7 17 7790 60Wh 3750mAh battery but after several charges, even with the Windows 10 Power Plan set to "Battery Saver" , it only lasts 2 Hours .I read on the G7 7790 official specs that with light use, not heavy CPU usage, like web navigation the G7 last about 7 hours  ! I also remember that with the previous Dell battery I had more than 2 hours, and I must say that I have not changed anything about BIOS, etc. Meanwhile I contacted the Dell support and they told me that the battery can be changed but it is very strange because all the tests of this current new battery gives me the resutl "Your battery health is OK" Looking forward to hear from other Dell users . Angelo   
Dell G7 7790 - Original 60Wh Battery ONLY lasts 2 HOURS !?!?