I use electronic muffs with foam plugs all the time, both indoors and outdoors. For me, it's a great combination.
When taking a class, or shooting with somebody else, I just crank-up the volume. Allows me to hear whoever's talking very well.
With electronic ear muffs, it's about (a) the design of the earmuff, and (b) the circuitry used to cut-off the impulse noise. You have to get a set of muffs that START with a good NRR (like I said in a previous post, the highest NRR rating is 33 and you can get muffs with that rating), and then the manufacturer has to spend enough money for good amplification and cut-off electronics. One difference *I* notice between using expensive and less expensive (the electronic muffs are pretty much ALL expensive) muffs is that with the less expensive flavors there's a noticeable lag after an impulse noise (gun shot) during which the audio sort of "fades" back in.
The only muffs I've found that have both maximum protection and good circuitry are the Pro Ears Pro Mag Gold muffs (the ones with the CR123A battery). They're ridiculously expensive, but not as cheap as trying to buy new hearing
In terms of low battery warning... hmmm... There doesn't seem to be ANY indication that the battery is low. I always carry several extra CR123's just in case.
Hope that helps, at least some.