@Nomi: There is no light of full battery but it surely won't damage your battery. It is a good inverter but it just doesn't have the bypass relay, rest is fine.
The inverter you have and the UPS i'm selling both have smart chargers and do not damage the battery. When the battery volts are 10VDC it automatically shuts down so that no damage to battery occurs, upper limit is 15.5VDC hence improving life of battery.
What the local ups people do is that they do not set any low voltage of battery parameter, all you guys have cars and you must know that any battery going under 10VDC and still your running music when the car is not running is due to be damaged. Same in the ups case, by not setting the lower limit you get 15-20min more backup and those hardly moving fan blades, but we say no problem let it run as long as its spinning. That is what causes damage to battery.
Converting it to single wire is not a good idea, i do not recommend that. But it may work if the electrician knows what he's doing.
You do not need to do the wiring again sir, its just 1 more wire running along the already laid wire, even you can do it.
I think now i have explained it in great details : ).
@tazzix: Yes you are right running anything except fans and tubelights on the local ups's cause slow damage to appliances. This ups is modified sine wave or line interactive. It causes no damage and you can run your laptops, chargers, tv's, computers, sound systems, you name it, it can run it as long as its not over 600W.
I can arrange shipping but how will you pay me for it? shipping charges are not included in Rs. 5500.