Actually, I used to work at a local Walmart, and the biggest problem is they don't have enough, except for overnight, they can never charge long enough, maybe one will charge for 15 minutes before another customer needs it.
@calicuz even the fully charged ones in the morning can wear down quickly when a really heavy person gets on them. There is a weight limit on a sticker on them but some people are probably 100 pounds or a lot more over the limit.
