As part of a crash effort to build two customer nanosatellites in two weeks, the reality of typical COTS lead times and a limited budget forced us to adopt a radically simplified approach to the satellite's power system. We decided to run each spacecraft solely from battery power, without any solar panels, etc. Pumpkin's BM 2 intelligent battery module is ideally suited to "battery only" missions, with an energy of up to 100Wh, SoC reporting, independent heaters, and various protections. At 14,000mAh, there's a lot of battery life in the BM 2. The BM 2's typical operating current is 20mA; when an EPS and solar panels are present, the cost of those 20mA is quite minimal. But for a battery-only mission, that's only about one month of operating, powered up, at quiescent currents.
In a spacecraft utilizing only battery power, a smart battery becomes the EPS, because of its ability to isolate loads from the battery's cells. Simple external regulators downconvert the battery voltage to more usable voltages like +5V or +3.3V. There is no need to switch power systems, since everything outside of the battery is unpowered while the battery sleeps.
To implement this functionality, we've added a new software feature to the BM 2 -- a sleep mode. When the BM 2 is sleeping, all power to the rest of the spacecraft is disabled, and the BM 2 maintains an internal "sleeping clock." With the BM 2 sleeping at around 1.5mA, a mission life of around 400 days is possible. Sleep can be commanded with single-minute resolution, with a maximum sleep time of 120 days (7200 hours) via a single command. When in a deep sleep, the BM 2 will wake up every two hours for one minute, giving the flight software the opportunity to cancel the sleep if desired.
The new BM 2 firmware is currently being tested, and is available to all BM 2s built on Rev F1 or later hardware.