Rechargeable graphite battery. One of my own designs, works well. Uses silly putty, graphite and play-doh. Copper and aluminum electrodes. These types of batteries charge fast and supply power a long time. But word of warning play-doh batteries off gas when used with aluminum so use in well ventilated environment, not for kids to make if aluminum is used. Video at https://www.youtube.com/watch?v=I2h3GPS7zhY

Personally Ive had a lot of big hits over the years and some are even in my videos here https://www.youtube.com/stevensrd1. You know how much big hits get you if you dont have any money to market it yourself, zilch, nada. I learned long ago free and alternative energy is not something you can make money on. I also learned that if you sign a NDA with the big wigs which usually states you keep your mouth shut about your own invention or idea, for a year, all they do during that time regardless of all the money they say you will make, is they steal your idea and sell it to someone else, as you half to keep your mouth shut about it because you signed the non disclosure agreement. And you get nothing. So now days I put many things out there for the world to do with as it pleases with hopes it benefits someone at least. I do have a fund raiser website up that also brings in about zilch. But I like having it up anyway because you just never know. Sorry about the truth of it all, many just have no idea how it really is.

Oh as to charge and run time, just the bare basics here. 10 to 15 minute charge can get you a run time from one to several hours lighting the light. Run times can be changed relating to how much is used in the mix between the graphite, play-doh and silly putty. Using more between the electrodes can change run time as well, also electrode size