When using it I've found that some smartphones (like my Droid RAZR) are very sensitive to fluctuations in the level of current. I went looking for a way to solve this issue with a buffer/cache battery and I believe I've found the perfect buffer battery that's A LOT cheaper than an E-Werk cache battery.

The Motorola P893 is 1800mA and small enough to fit inside bento boxes. It's tiny, light, supports charging of 2 devices concurrently, and can be recharged at the same time it's charging other devices. I'm going to try it out powering both my front hd808 and my razr. I'll report back on how it works.