Ill try and keep it short.

Basically Im trying to run my Makita dropsaw off the van battery.
I used the power meter to test the wattage of the saw off the house mains, for about 2 seconds it runs at 1450watts then once its up to speed it drops down to a stead 450watts. I didnt have anything handy to cut but im sure power usage will go up when cutting through something.

Inverter is a 1000W continuous, 2000w peak
Now the instructions that came with the inverter were not specific at all, no installation or trouble shooting on it (its only 1 page) WITH the exception that it says if its was over a certain wattage it had to be direct wired to the battery. (generic instructions for smaller ones)
I have wired it up directly to the battery using the cables that came with it.

Ive procrastinated about 3weeks before writing this, and it works fine for charging batterys or anything else. But it wont power up the drop saw.

The batterys in the powermeter thing are flat, so it only turns on when plugged into the power.
When I try and run the saw, it powers up for about 1/2 a second then stops for about 2 seconds then powers up etc etc it loops.
The power meter gets too 700watts before the cutout, and then the powermeter turns off, so power is being completly shut off.
The saw does spin a little faster each loop but seems to peak, never reaching anywhere near full speed.

Im trying to trouble shoot why the inverter isnt 'peaking' to 2000watts like it says it will. The manual doesnt say how long a 'peak' should last, but I though 2 seconds should be within the time

Perhaps the 12volt battery cant take the required output? Altho its not flattening the battery as it still starts fine.
I have tried having the van running with idle control set to 3000rpm (its a diesel, so pretty high)
I tried to get a photo of it, but perhaps the connection of the red wire into the inverter itself, doesnt look like theres a lot of contact. Tho I show do it.

Has anyone else tried something like this?
In an ideal world id like to have a UPS to take the extra strain, but the price on one that will put out 1500watts is expensive, for something I only want 2 seconds of work out of

Edit: forgot the pictures.