This might be something for SparkFun to look into but maybe @BDub can also comment here (and more importantly in the GitHub issue for safe keeping and ease of reference)
It would be useful if the controler on the shield would only allow a power-up if the battery got beyond a certain level of charge that will allow the device to properly work at least for a few minutes.
I’m quite sure there is a hysteresis set, but it might need to be increased and since the controler can’t know your external circuitry, which might outweigh the Particles own power consumption and hence render the set hysteresis too small again, it might also be useful to allow for the user to twiddle that setting to fit the hardware setup (with documentation ;-))