I'm guessing you got a deal on the site, so talk to him and come up with a reasonable amount.
Even if he did agree to include electricity, if it's costing him a lot more than he expected, if you tell him to take a hike, he is likely to tell you to take a hike as soon as your lease is up.
It's a bit confusing why you brought up (or bought for that matter) 3 space heaters if you only use 1 for a couple hours in the morning.
Each device you use will have a rating on the UL lable. Most will be in Watts. Divide by 1000 to get Kilowatts. Then multiply Kilowatts times how long it is on. For the fridge, water heater & battery charger just make an assumption (maybe on 50% of the time). Multiply them out and add them up. That's how many KW-hr are being used or at least a rough estimte.
Power companies typically charge from 6-30cents for each KW-hr used. Lucky you California has some of the highest rates in the country.
Now if you had 3 heaters at 1500watts running most of the day, that can add up to a pretty big bill but if you only run 1 for a couple hours in the morning, it shouldn't be a huge bill. I would figure everything together maybe $50-75.
By the way lights and TV for 3-4hrs at night should cost hardly anything. 3-4 bulbs at 10-15watts and a TV at maybe 50-100watts is negligible compared to a heater at 1500watts.
