So it turns out that the folks at Commodore didn't think the amiga would still be around 25 years on and only made batteries to last 10+ years.
The result on the 500plus models is as in the pic. The expansion on the older 500s had a battery too.
Be cheaper to get a new mother board, but where is the fun in that.
There is a company who have done a run of new 500+ motherboards.
I found quite alot of info so should be able to repair it.
I'll post it up here in case it helps anybody else.
Once its fixed i'll chuck it back in the garage and forget about it for another 20 years.
I ordered some bits to make a start so lets see how it goes.
could always put an emulator on the android box that, runs on hdmi too.
when it turned it on the power light flashes 10 small and one 1 longer flash. According to the internet go to try reseating the agnus......
when left on for 5 minutes the chips get warm to the touch except the gary, the one near the battery accident so starting there.