I bought a laptop fairly used dell Verizon 3550
and I noticed when charging it stops at 49% it also drains fast (the battery).
so I decided to buy another battery yesterday .charged it to 100% now the problem is when using the laptop the battery drains to 50% then jumps 7%(Low Battery) please is the fault from the laptop or battery??

Vanwhizyy:
I bought a laptop fairly used dell Verizon 3550
and I noticed when charging it stops at 49% it also drains fast (the battery).
so I decided to buy another battery yesterday .charged it to 100% now the problem is when using the laptop the battery drains to 50% then jumps 7%(Low Battery) please is the fault from the laptop or battery??

first of all Go back to place where u bought the battery for them to change the battery for u and make sure u charge the new battery at least six hours before using it .
Mostly this problem comes from battery
And at times it might be the power settings in windows

Are u using windows 7?

likely from your battery
mind you you also need to check your charger too
but in this your case the battery is likely to be the issue i have experienced something like this on my dell 3330
check out this article on how to know original battery to avoid been cheated next time

https://9jatide.com/2020/04/how-to-differentiate-between-original-laptop-battery-and-fake/

also check your battery life using an application in that article link above it tells you alot about a battery before buying