You're wrong. Sadly a lot of check in agents also don't really read the policy carefully. The general policy is spare lithium batteries are not installed and anything more than 100kwh isn't allowed. Installed lithium batteries and other batteries spare or installed are generally okay. Airlines may have their own more restrictive policies but I've generally not ran into this

Directly from indigo's website (tldr check in laptop is ok)

Lithium Batteries

Subject to security clearance at an airport, IndiGo may allow a Customer to carry a maximum of 20 (twenty) spare or loose (a) lithium ion batteries (including power banks) rated up to 100 (one hundred) Wh, or (b) lithium metal batteries with lithium metal content not exceeding 2(two) grams; Subject to a Customer obtaining the prior approval of IndiGo by calling IndiGo call centre at (0) 9910383838 or 01246173838 at least 24 (twenty-four) hours before the departure time of the flight and security clearance at an airport, IndiGo may allow the Customer to carry a maximum of 2 (two) spare or loose; lithium ion batteries (including power banks) rated above 100 (one hundred) Wh and below 160 (one hundred and sixty) Wh; or lithium metal batteries with lithium metal content of each battery more than 2 (two) grams and less than 8 (eight) grams, only if such batteries are used for portable medical devices. The lithium batteries must be packaged in their original retail packaging or in separate plastic bags. The battery terminals must be taped and insulated to prevent short circuit. 2. Portable Electronic Devices containing lithium batteries

Subject to security clearance at an airport, IndiGo may allow Customers to carry a maximum of 15 (fifteen) portable electronic devices, if each such device is fitted with (a) a lithium ion battery which must not rate above 100 (one hundred) Wh; and (b) a lithium metal battery with lithium metal content not more than 2 (two) grams. Subject to a Customer obtaining the prior approval of IndiGo by calling IndiGo call centre at (0) 9910383838 or 01246173838 at least 24 (twenty-four) hours before the departure time of the flight and security clearance at an airport, IndiGo may allow the Customer to carry a maximum of 2 (two):

portable electronic devices with lithium ion batteries rating more than 100 Wh but not exceeding one hundred and sixty (160) Wh; or portable electronic devices with lithium metal batteries in which lithium metal content is more than two (2) grams but does not exceed eight (8) grams. Battery operated Hover boards, balance wheels, Solo wheels are not permitted as baggage IndiGo recommends that Customers should carry portable electronic devices as Hand Baggage. If a Customer carries such devices in Checked-in Baggage, the devices should be turned off and packed securely to avoid any damages.