They have to be banned unless regulation-use batteries are used, simple.
Registration maybe required as someone will die otherwise from use of unregulated battery explosion
These batteries are invariably imported from places of doubtful reputation. The makers will apply whatever approval marks or certificates that are required for the intended market. including CE marking, UL listed, or any other standard.
Better regulation and clearer laws will no doubt help - the current free-for-all cannot continue.
If you pass laws that make JustEat and the like directly responsible for ensuring their riders use proper equipment (perhaps by supplying it, or offering incentive schemes through approved retailers) and don't break the law then that will help enormously
IMHO▸ . Forcing them to provide proper contracts of employment rather than treating them as contractors and letting them get on with sourcing their own bikes and (lack of) equipment will also help. Being paid per delivery only encourages them to buy unsuitable equipment and ride it irresponsibly.
It might end up making their businesses unviable which is tough.