user15190: Is it allowed to have battery and USB connected to the Trinket(3.3V) at the same time?
I am using the battery to also power other components, so always disconnecting power, hooking USB to re-program and vice-versa is quite time consuming (and I fear to ruin the connectors).

user6628: From https://learn.adafruit.com/system/assets/assets/000/010/773/original/adafruit_products_trinket3.png?1378223258 it looks OK -- there are blocking diodes D3 and D2 that prevent backfeeding either the battery or the USB +5.
If you are worried, or want to monitor battery-only performance, you could make a special USB cable with the +5 red wire disconnected, and rely on the in-circuit battery to power the device, while still using the USB data lines.  See https://www.pjrc.com/teensy/external_power.html Option 2 for an example of the cable surgery.   

15190: <p>Is it allowed to have battery and USB connected to the Trinket(3.3V) at the same time?</p>

<p>I am using the battery to also power other components, so always disconnecting power, hooking USB to re-program and vice-versa is quite time consuming (and I fear to ruin the connectors).</p>
 6628: <p>From <a href="https://learn.adafruit.com/system/assets/assets/000/010/773/original/adafruit_products_trinket3.png?1378223258" rel="nofollow">https://learn.adafruit.com/system/assets/assets/000/010/773/original/adafruit_products_trinket3.png?1378223258</a> it looks OK -- there are blocking diodes D3 and D2 that prevent backfeeding either the battery or the USB +5.</p>

<p>If you are worried, or want to monitor battery-only performance, you could make a special USB cable with the +5 red wire disconnected, and rely on the in-circuit battery to power the device, while still using the USB data lines.  See <a href="https://www.pjrc.com/teensy/external_power.html" rel="nofollow">https://www.pjrc.com/teensy/external_power.html</a> Option 2 for an example of the cable surgery.   </p>
