So we accidentally put the cables on backwards (red to black visa versa). Then tried to start the vehicle. Obviously fried something. Now totally dead when trying to jumpstart correctly. How much damage can I expect? I’m hoping there is a fuse that protected me from my mistake.

2009 Accord 3.5L EX SEDAN

 

You'll have to look for what's burned. Especially look at the large fuses, like the ones that are fastened into the fuse box with screws.

Also, check whether it ruined either or both batteries. Just connecting the 2 batteries in series with each other would draw a very large current through the jumper cables, and maybe just fry one or both batteries.

Did you use a normal car battery as the booster? Or one of those rechargeable booster packs?

I'm moving this over to General Tech where more people will see it. The "new member" area is mostly for welcome & introductions.

 

Thanks for replying. I used a booster pack which seems to be fine.
I’ll look for fuses.

 

It would be the under-hood Fuse No. 1 (large multi-fuse) and driver's side under-dash Fuse No. 7 (5A). The No. 1 fuse for a V6 is different than for a L4 engine.

 

You were spot on, also needed a new battery of course. Thank you so much!