Is it ok to power the Moteino 8Mhz variant (with radio) with a single cell LiPo? When fully charged Lipo cells exceeded the 3.6V warning on the Moteino page (around 4.2V). Thanks for any help.
max operating voltage is 3.6v, so no, you can't use LiPo as is, but you could use lifepo4
You can use up to 5.5V (max atmega328p limit) but only if the Moteino-8Mhz is without a radio module and without FLASH !
Technically this defeats the purpose of the board, and at voltages of 5V you can run it even at 16mhz (with the included onboard resonator, by changing fuses).
If a radio module and/or FLASH-MEM are installed, then you can feed it a max of 3.6v.
Generally speaking, the Moteino-8Mhz was created to be used with radio modules at voltages below 3.3V, to enable even lower power savings, it can go down to 2V and still work, some forum users reported 1.8V and even 1.6V (if I recall correctly) still pushing out RFM packets. At some voltage point even 8mhz will be "overclocked" but it seems to work OK (see 328p datasheet for exact limits), just as 16mhz works without a glitch at 3.3V (on the regular Moteinos).