What do you mean by a lead sealed battery?
Essentially both, I'm assuming you meant a sealed lead/acid battery, are the same with the biggest difference of how the electrolyte is bathing the lead plates. The gel cel just means that the electrolyte is a gel. The gel battery is smaller so you can install it inside the box if you want. A sealed lead acid battery is larger and heavier but stores a lot more amperage than a gel cel, 15amp/hours and up beyond 500. Gels usually come in 4.5 amp/hr or 7 amp/hr and are for hobby use not for a trolling or starter motor.