Electricity - Battery bug?

Hi All

At the risk of making a fool of myself. I think there might be a bug in Electricity batteries.
If I am wrong, sorry for alluding to it, its always possible it is my mistake.
Or maybe its just a allround known issue, but I did not see it.

In short:
4 Large Batteries , fully charged, and their outputs are combines. (so they are able to offer 400W)
If you have 60W worth of lamps on this output, you will see that each battery gets drained for 60
And not each battery for 15 (1/4th) as you would expect

I noticed this when my batteries kept getting drained and my Power creation(300) was larger than my usage (150)
But now with this, I notice my consumtion is 150 PER battery, 600 total

Anybody some feedback ? known issue? or am I just dumb?