How is the vehicle power cost calculated?

I have a fully charged (300MJ) receiver and it tells me "The destination teleporter Beacon does not have enough energy (88% of needed)" when trying to teleport the spider.

The only mod that I could see interfere with this would be VehicleGrid 1.4.0 - but otherwise I run no gameplay altering mods.

Cost for vehicles is explained in the changelog - 10% increase for each weapon slot, 1% for each inventory and equipment grid slot. VehicleGrid is probably increasing the size of spidertrons grid, and vanilla spidertron takes up almost the entire buffer as is.

I’ll probably end up allowing teleporter equipment to make up the deficit in the next update, but for now you’d have to use the teleporter shortcut instead of beacons with it. At the least I’ll look into a specific message for the max charge not being enough.

Perhaps add a research tech that increases the buffer. It could be neat to have even without this issue, to allow for more frequent teleportation if one would want that.

Factorio's engine generally doesn't allow that sort of thing without weird hacks, fortunately beacons are already using a weird hack to store energy so it's actually feasible to do that with an infinite tech to increase the buffer size per level in a future update.

As it is, 1.1.8 includes a specific message if the buffer isn't large enough in the sending/receiving beacon.