How many autobots died in the Battle of Autobots City?

Nothing BUT G1 characters died in that movie considering the series is retroactively known as G1

Maybe you mean season 1 characters, because many of them were rubbed out as of the movie, and any survivors were phased out afterward

the comfirmed body count is 8:
Brawn, Prowl, Ironhide, Ratchet, Windchager, Wheeljack, Huffer, and Optimus Prime
Other uncomfirmed and dropped storyboard deaths are:
Mirage, Trailbreaker, Smokescreen, and Red Alert

Autobots:
Optimus Prime
Wheeljack
Windcharger
Prowl
Brawn
Ironhide
Ratchet

Decepticons: None died in the battle, but later reformatted by Unicron into new Decepticons.
Insecticons - Sweeps
Thundercracker - Scourge
Skywarp - Cyclonus
Megatron - Galvatron

Autobots like Huffer and Bluestreak who were outside of the city when the battle started, were not confirmed as killed in the battle, though Huffer's remains were shown as being placed in the Autobot masoleum in the third season episode, "Dark Awakening."