Update or the long story short! - Went to electronic street (Cochin, Kerala) and checked few shops. No luck! While returning, saw a repair shop and thought I will check with that guy. He was kind enough to spend some time asking my exact requirement and details of battery etc. Asked me to sit and explained why it may not be a good idea to buy a heavy duty charger. Instead, he took something from the service area which he built himself and told me how it works.
Basically it is a charger but pretty small and produce 12V. We need to connect this to battery which need to be charged. Then switch on the inverter! As the inverter see 12V, it will start charging. Once the voltage is up and manageable by inverter, we can disconnect this charger.
Reading more on it in internet, looks like a good idea. Yes, it will not work in all scenarios. Like water is drained or voltage is too low. But I have a feeling that it will work for my use case. He is ready to build one for me, and after talking for sometime, he is even ready to have it for few days (rent may be, still a good idea) when I go village home. Liked the guy as he wasn't forcing me on anything but explaining things in a pretty simple manner.
I see such small chargers are available online too. May buy one of those, or will check with this guy.
Thought I will share the info.
