BTR15 which is the updated model of the BTR5 might be better if you’re worried about the battery charging and discharging. It is unreleased but it is announced and should be coming soon-ish. It also has a few other upgrades if you want to look at it.

Foam tips but it’s not the same. But the problem with customs is they don’t fit well since iems have many shapes and nozzle sizes. Usually customs eartips are made of some sort of silicon. If the nozzle of the iem is too large, it’ll be a bad fit. It actually could get slightly uncomfortable if the fit is off.

Hexa has one of the larger nozzle sizes. The zero is slightly smaller albeit large still. If all the eartips simply slip out it should mean that the eartip or maybe the nozzle is far too large for you or you’re not setting the iem deep enough. You might have more success with something else since your ears just aren’t accommodating. I had similar issues with my left side of my ear with every iem since it’s more narrower and was much trickier to find eartips that fit. Just know that you may need to rock different size eartips for your head.