I hate units with built in Lithium batteries. I tolerate it on my GPS unit in my car, as I don't really expect to use it for any extended period as a pedestrian. I tolerate it in my smartphone because after the built in battery ages a few years, I will most likely simply get a new smartphone from my wireless vendor at a significant discount!

But I would hate to think that a speedlight goes useless after three years because the capacity of the lithium anode has deteriorated and lost capacity (lithium begins to age as soon as it is manufactured!!!)