I am in same position

what we have is a set of straps to tie them down

as part of or job sheet we have a waste carrier form to fill in for our
waste oil rags and filters.

There has been a change to the law regarding Lithium batteries with regard
to HGV so they now are having to display the warning decal saying that
they are carry them. So I don’t know if you may need this

If you only have one or two and in good condition, I would ensure they are strapped in so they can not move at all. New or old I would ensure that at least one terminal has a protective cap to stop anything touching both terminals together (even an old one can explode). I would ensure nothing else in the van can float about and damage the battery. If the battery is damaged, I would have some form of full height plastic container and strapped (watch out for manual handling issues here as these things are heavy). Lastly if you are carrying waste batteries back you need a licence to carry waste (lower tier to carry your own waste and yes, it is your waste as you changed it with a good one. Lower tier = free). Have something appropriate in the first aid kit in the van.

Lastly have some sort of spill kit just in case of a leak and something to put used kit items in until return to base.