I am preparing my hobby project in audio and I need a slim 7.4v lipo battery (less than 13mm in thickness) that can fit into the bottom portion of my pencil box. Mostly the airsoft style batteries fit my application better.

One battery that interests me is:
https://www.gensace.de/gens-ace-25-50c-2700mah-2s1p-7-4v-airsoft-gun-lipo-battery-with-t-plug.html

Honestly, 1500mah or 1800mah is more than enough, provided the manufacturer isn't faking the specs but if the higher capacity could be done in under 13mm, I would take it.

Have been searching for a while and general consensus seems to be that gens ace is very good. Have also heard good things about china hobby line and tenergy. I am however unable to find where to buy these in India, especially airsoft batteries. Would love if anyone can guide me both on the battery alternatives and also where to buy the reliable ones in India.

Thanks in advance.

you can give NOKIA BL-5C batteries a shot. These are 1000mah and only 5.3mm thick, so you can set them up in a 2S2P configuration, and get your voltage and current required.

Airsoft batteries or anything airsoft related is very difficult to find in India, so this looks like a viable solution for your problem.

I have used BL5C batteries in the same configuration for years in my Tx without an issue, so I can vouch for that

Regards, do keep us posted

https://www.amazon.in/Nokia-BL-5C-Battery-Original-product/dp/B000RUM55Q

In the hobby field, most batteries are more about length and width. The only thing I can recommend is a 1000mah 2s, which is only 10mm in thickness
https://www.ovonicshop.com/products/ovonic-7-4v-2s-1000mah-50c-lipo-battery-pack