Which laptop should I go for? I have a budget of about 40,000 and I am looking for a i5 8th generation laptop which have a good battery backup and specs. It should have a good longevity. So, should I go for ASUS or Lenovo or HP.

Going for an 8th Gen CPU is not recommended because it’s now outdated. Intel has already launched 11th Gen CPUs in the market.
Your budget is very tight for an i5 processor laptop. I suggest you look at increasing it a bit. One option is the HP 240 G7 1S5F3PA. The laptop has modern security features and is equipped with 10th Gen Intel Core i5 CPU, 8 GB RAM and 1 TB storage. The 14-inch laptop has a thin and light profile. It has a durable chassis that protects it from daily shocks and jolts. It costs around Rs. 54k without Windows OS.
If it’s difficult to increase your budget by so much, then consider going for an i3 CPU based laptop. One option is the HP Laptop 15s-du2071TU. It comes with a 10th Gen Intel Core i3 CPU, comes preloaded with Windows 10, 8 GB RAM, and 1 TB HDD. The laptop has 15.6-inch FHD (1920 x 1080) display and comes pre-loaded with Alexa and Microsoft Office 2019.
Asus, Lenovo and HP are well-known brands, but between the three, my recommendation would be to go with HP, due to its wide service network and a host of offerings on its laptops that are not available in competing products. For instance, HP covers the battery and power adapter in the warranty, which is not covered by the competition. HP’s business laptops come with 3 years onsite warranty, which again is unique.
If you’d like to learn more about which laptop or printer/scanner is right for you, then check out the tech4growth section on dqindia website or the nextgenit section on ciol website.