Lead acid batteries need to be level for proper opperation. Out of level
will cause uneven wetting or the plates over time. I'd bet it will
eventually start to leak if the slant is very great.

"A.Z" wrote in message
om...
How important is it for the battery in a boat (18.5, 90hp outboard)
for the battery to sit flat on the floor? The replacement battery I
just bought does not fit in the battery case, and I had to install
with it sticking out at an angle.

André