I'm getting a lot of conflicting information on trickle charging. Some places say it's fine, some say it reduces the life of the battery. I'm thinking I'd be better off doing something like:
1) Discern approximately how much battery power is used per second.
2) Have GPIO set up to sense when power is lost (opto-isolator with 5v from PSU on one side and 3v3 pin to GPIO input on the other)
3) Enable the trickle charge of the battery for an amount of time equivalent to the power lost (say with GPIO output going to a transistor)
4) One every couple of days or once a week or once a month, keep the trickle charge on for a full day or two to ensure battery is topped off
5) Alternatively, run an LED off the battery every so often to make sure it's discharging more than just a percent during random power loss
I'm looking into this option I found on ebay
http://www.ebay.com/itm/PCB-Charger-mod ... 3cba39cefa
It seems like it is specifically designed to be used with the 18650 Li-ion battery which supplies 3v7, but it claims to be compatible with NiMH which means in theory I can take two NiMH, wire them in series and get enough voltage to fall within the parameters of this board... of course then I have to worry about them charging evenly. I might just come out ahead getting the board and a single 18650 battery
Thanks for the input thus far, it's helped!