I think that's how some HSMs work to guard against tampering. The keys are stored on volatile memory, and there's a internal battery/capacitor. You can unplug it, but its tamper intrusion mechanisms will still be active because of the internal battery. If you trip the tamper detection mechanisms, the keys get wiped. If the battery runs out, the key gets wiped. So if you're relocating the HSM, you have x days to replug it in before you lose your keys. I imagine if you're designing a high security phone, you could possibly want this as a feature, but I doubt most people want a phone that wipes their data if the battery went flat for 7 days.