I appreciate @x475aws, you might pay closer attention to a 312 battery, as opposed to a 675, the runtime is vastly different… I just wouldn’t use a battery gauge, even if it where highly accurate, it wouldn’t float my boat, but each to their own… Zinc Air, just works, and it works well… I am highly interested in LiFePO4 Lithium Batteries though, I have literally thousands of pounds worth, and because they are extremely expensive, replacing them is cost prohibitive, so I like to take care of them, I have approximately 21kw of of LiFePO4 rechargeable battery bank, with 4kw of solar on my house roof, on top of that, all my Dewalt tools run on either 18 volt, or 54 volt rechargeable batteries, I have at least 6 chargers, and about 20 batteries, between 4ah & 6ah, you could say, I am am a lover of all things rechargeable, with one extreme omission, I do not (as yet) rate Lithium batteries worthy of my hearing care needs, but I am certain at some point in the future, they will make an “Ultra Power Hearing Aid”, with an excellent runtime, (Perhaps 2 to 5 days) with easy access to replace a Lithium rechargeable battery, so we can hot swap out, with a replacement recharged battery… When that day shines, I will be first in the cue, Cheers Kev 