It's surprising how many aircraft experience power failures. Redundant systems addressing this can often be costly, complex and heavy. One way to keep flying safely without adding a lot of weight, complexity or cost is to simply add an optionally available internal back up battery to the EFIS or FlightDEK itself. This battery will automatically take over powering the instrument should main power fail, thus enabling continued flight until you can safely reach the next airport.
The battery and charging circuitry are conveniently encased within the EFIS itself and automatically charge that battery anytime external power is applied. A separate, user serviceable door on the instrument case facilitates easily battery installation and removal at any time.