Funny thing is I have a plain 15W panel, used to charge SLA batteries to camp, so that we can have light at night, and not run a generator or make car batteries dead. No charge controller, work in progress, but before Christmas power was out for half a week due to the substation being vandalised, so I needed to power the gate motor, so put this across the battery as it was, and the 0.8A charge kept it going for most of that time with no mains power. Estimate to charge the battery fully it would take a week, but it kept enough charge in to keep it partly charged.
What OP wants is basically a solar power bank, any number of them around, some good, most cheap and, as Dany would say, "Sooper Dodgy", and you just buy one off the river site, or off of the slow boat from the express, and guess the specs are overstated, safety is something they heard of, and quality control is "it did not blow up".