Humans don't put out much power. Here's a foot or hand cranked human powered generator:
Puts out between 3-5 amps. So you would be able to recharge a dead 30ah battery in oh...10-15 hours or so of cranking on the thing.
Maybe you could get two and do both hands and feet for a nice 8 hour full-body workout. Only $550 each.
Current: 76 E-250, bubble-top, self-contained|couple of old Yamaha enduros
Previous wheelers: 41 Willys|78 FJ40|78 Bronco|84 Bronco|74 Ramcharger|78 Ramcharger|79 D150 PowerWagon|77 D100|79 D400 dually, converted to 4WD, utility bed, 10' Lance|75 Westy|69 Scout, RHD|bunch of others|bunch of bikes|couple of boats|couple of motorhomes|blah blah|so what|not my idea|just doin' what I'm told|wank wank|this space for rent|candy is dandy|but liquor is quicker