Reconnect the battery connector track side up.

Put lid back on battery, being careful not to trap the cable. Push closed all around.

At this point you can test the battery. The battery bolts will be annoying to lock in place without the rivets to guide them but it is possible. If you have a multimeter should hopefully get you two of the pairs of contacts giving roughly 12.5v each from fully charged cells.

Now the fun part... I never managed to find replacement rivets. If you can find 12mm(head)x8mm(outer)x7mm(inner)x10mm(long although you can cut down anything longer) rivets... you can use them.

If you can't... And because the rivets also act to guide the retaining bolts so make life a lot easier...

You do what I did and get 8mm copper/aluminium pipe with an inner wall of less than 0.5mm or (I used 0.25mm because it was half the price.

I then used a mini pipe cutter to cut approx 14mm lengths, used side cutters to cut a few 2-3mm cuts at each end, put it through the holes, and then bent those back like petals to make crude rivets.

Put the bolts back through the holes, put the circlips back on, bend the circlips so they retain the bolts again. Reapply your rubber seal. Sometimes it will be harder to insert the battery if you have to use the homemade rivets. This can be eased by replacing with a thinner good quality foam tape.