I have the same issue with my GS300h. I don't think there is any way to open the boot until the battery is charged. However, I have discovered that there should be a Positive terminal in the Fuse box under the bonnet- but there isn't. If you can find it connect the Negative to an earthing point/bolt and jump start. It says that you should continue to receive the charge from the second motor for some time in order for the battery to top-up.. The battery fires up the computer, without which you can,t start the engine. I'm looking for someone to tell me where the Terminal is for my car, as I haven't yet found it.