I'm familiar with that engine - the 2001 Pontiac Montana I used to own had its battery in a similar place.
Its a total pain in the ass to get to.
Its behind the headlight. You'll need to remove a couple of other things to get to it first. A support strut in the corner of the front frame, the washer fluid reservoir. You might need to move the fresh air intake hose as well.
Larger GM 'luxury' vehicles of the same era tend to hide the battery under the back seat. - and honestly, those are far easier to access. -Grab the back seat where it meets with the seat back, pull it up and flip it forward.