sorry to burst your bubble, but I wrote about this exact problem about 7 or 8 years ago on this forum.
The battery bank will degrade and die off eventually and will cost a fortune to replace because there is zero local support for these cars in Pakistan. You can have the cells tested and worked from other scrap items one or 5 are bad but other issues like people using tap water to cooldown inverter is also a problem - Once it internally rusts, then its game over. People in Pakistan are known to use tap water in the inverter and also engine cooling system because "jenyan koolent mehenga hai" or if someone is feeling very benevolent they will add green osaka coolant which will gel the original pink coolant and destroy your car.
The engine used in prius/aqua is very gutless due to being small and atkinson cycle, It doesnt have enough torque on its own to pull a heavy car like a prius/aqua as efficiently as an otto cycle engine would. So you cannot just drive it on its engine.
The reason you dont see the problem without A/C is because the A/C compressor is electric on your car. The battery bank is not getting discharged as quicker as it would with the A/C working.
Get the battery bank worked out - check the coolant condition for the inverter, if you see that its original but old - prepare to buy a new inverter pump (dont buy scrapped item for this - Toyota updated the pump with new number). - If you see the cooling liquid is water or gelled or is rusty, expect another big hit on your wallet in the future.
