I have a circuit with a sealed lead acid backup battery, which it charges automatically with a constant current of 350mA at ~15V.
I wish to connect an additional module to the circuit (gsm gateway) which draws between 50mA and 150mA, with peaks of 2A when sending an SMS or communicating through Wifi (periods of seconds), at 5v. DC-DC step down will be used.
That is: the charger would be providing 350mA (~5W) to the battery, and some of this current (~1W) would be diverted to the gateway. I assume the battery would automagically be providing energy for the short peaks (~10-12W). DC-DC step down efficiency will be higher than 75%.
1) Considering that most of the time the gateway will be resting in low power mode, what is the short and long term effect of connecting the gateway in parallel with the battery?
2) Is this potentially safe for the battery and charger?
3) Without power failures, would the battery still be mostly at 100% charge? I assume the duty cycle must be analysed.
4) From a system engineering point of view, would it be substantially better to have a >16v (higher than charger) power supply in parallel with the battery, protected by schottky diodes, or a power multiplexer? Battery recovery time would be better, but the number of components, power dissipation and space required would also be higher.