Determine max voltage input of Bluetooth headset hm1100?

[salil]

I'm trying to find out what the maximum input voltage is that Samsung HM1100 Bluetooth headset can safely handle via the battery terminals. 

Is there anyway to determine this without a schematic or any documentation? (I couldn't find any)
The HM1100 has a single cell li-ion battery which I want to replace with a power supply, but all I have is a 5v power supply, so I'm wondering if I can get by feeding it 5v without killing it (and not needing a step down converter)?  The cell is about 4.2v fully charged, but the 5v power supply I have is 5-5.5v.  Any thoughts?

Ps: I'm not using the hm1100 as a headset, just using the circuit for activating a garage opener.

[AndyC_772]

Is there anyway to determine this without a schematic or any documentation?

You could buy a large number of them, set them up with power supplies of different voltages, then run them for a long period of time and note which ones carry on working and which ones die 

An easier way might be to put a silicon diode or two in series between the power supply and the device.

[aveekbh]

If it charges using USB, can you connect the 5V supply to it? I'm a little unsure if you can connect to it while it's charging.

Are you using the garage door hack from http://hackaday.com/2011/06/15/an-even-simpler-smartphone-garage-door-opener/ ?

[salil]

Well, I think I found out the hard way, accidentally ran 5v into the HM1100 and it no longer functions :/  Oh well, fortunately I bought two.  Just FYI for anyone, don't feed it 5v directly to the battery terminals!