OptiPower: 3.500mAh 2S 40C Lipo
Lipo batteries come in all shapes and sizes. I use these 3.500mAh 2S as receiver packs, plugging into any of the Powerboxes that I always use in my large models.
I continue going for the OptiPower brand even for low current receiver/servo applications simply due to their proven track record which I have already experienced with their larger packs. After all, just because the receiver is less power hungry than an electric motor, it is no less important!