The issue I can see you having is that batteries are fairly heavy... It may be alright you holding the battery in place to test fit for size, but once you have fixed the battery to the lid you are going to have a lot of weight in one particular area... Which could result in the lid pulling in one direction...giving you additional neck strain or making your lid sit 'daft'
I understand your issue with longevity of battery life, but the smaller aa or square batteries will allow you to better distribute the weight and also take up less space...
Plus how long would it take you to swap out the batteries ( carried by your faithful crew of course) during actroop break... 30 secs???
I thought you were going to post some slimline mobile phone type battery when I saw your post... When I looked at the pics , it looked about the 1/4 size of a car battery... Lol
And yes you can use 'piss on your chips' , you never heard that before?
Variation on the 'rain on your parade'....
Good luck , would be interested to see it in situ and how the balance in the lid is affected...