Was I overcharged by the mechanic for battery charging?

So my battery has been drained and couldn't start in my house. I went to the nearest auto and asked how much would a battery charge be with home service. It's 100 for charging then 300 for home service.

Dinala yung car sa auto then after a battery load testing for 20 mins. Car's all fine.

Afterwards, I was charged 800. I thought it's only 400 since that was the initial price. Apparently the cost of labor is 400 as well?

Is it overcharging? It's my first time getting my car checked on the auto.