This thread got me to wondering so I had to go out and see what size battery I had in my igniter. I always thought it was A 2300mah but it was only A 1300mah. I tend to forget it's on the charger and leave it on for days, I would like to say it's an age thing but I always forgot them so it's just A me thing.
Anyway, I don't leave them on the engine very long and they seem to last me A long time between charging.
A safety thing here, I have had and seen them shake off the engine, hit the prop and go flying off into space. I have also seen the leads from the igniter run off the power panel get caught by the prop, that gets ugly real fast too.