Just a switch with indicator light...don't need the charge indicator. IBEC seems like a clean solution too though I like the redundancy of a separate battery circuit.
please do not be offended, i am only wanting to bring up a point. you mention you like redundancy. we all do. but why have three batteries when you can have two?
The CDI on a flight, depending on the engine/brand/cdi, will not consume more than 100 maH in a 10 minute flight, and this is with a DA 170 cc motor. but, back to my point, if your radio will not work, let's just say, do you not want your motor to shut off anyway? just go with the two!! get an IBEC. it is different, let's say, the radio redundancy from having two batteries plug into one or two receivers. if one receiver fails, you still have the other one, you may still have a chance to land it. if one battery fails, you may not even know it til you go to recharge it. see what i mean. if the ignition battery fails, you will still have your radio working. but, if your two radio batteries fail, you will lose surface control and the motor. But really now, what are the chances of that happening? As soon as you buy a new set of batteries, get a sharpie, and write your date of purchase on there. keep a flight log and keep track of how many flights you have on that airplane with those batteries. This is the way to avoid surprises. stay ahead of the game. If it was me, which i did do, i got rid of all battery ignitions over 1.5 years ago, and have never looked back. Have never had a problem with the Tech Aero IBEC. it will save you lots of problems to get rid of that 3rd battery. This is my 2 cents.