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If I were to implement a simple battery backup system like this to power several WiFi radios in a field situation, how would the battery handle it? Would trickle charging it like that wear it out after several months? Or years?

For example, the system could have power for perhaps three or four months, and then need battery backup for half an hour if the mains power went out.

I have seen some battery systems that monitor the battery's charge, and when they do charge it, they use a pulse system.

Do I need something like that? Or will this simplistic approach be effective?

BTW, this is a standard 12v Lead-Acid battery like from a UPS.

schematic

simulate this circuit – Schematic created using CircuitLab

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As Mrs Beeton would say - first catch your battery. The sealed lead acid type used in a myriad of long term applications such as UPS and alarms. Generally this battery is designed for exactly this type of application and will maintain its charge losing something in the region of 40% over a period of 1 year. (Some do better, some do worse - check manufacturer's specs. It also depends on other factors such as temperature etc. etc.) You should expect a few years of service before changing the battery. As your running a wifi system why not send data about battery condition.

The trickle charge only needs to keep the battery topped up. Overcharging is always a potential problem so the trickle charger should have limited voltage.

The circuit you have shown would not work as it does not switch between the normal supply and the battery backup. You need something like this. Reg 1 limits the charge voltage and R(trickle) the charge current. The LED indicates the supply is on (and ok) Reg 2 is the normal regulated supply controller. The diodes allow the battery to take over if the supply fails. (switchover)

enter image description here

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  • \$\begingroup\$ You would probably want to disconnect the battery somehow when the voltage gets too low to avoid deep discharge of the battery. \$\endgroup\$ – Johan Apr 8 '15 at 8:12
  • \$\begingroup\$ The battery should be floated at 13.7V when used in a standby mode (as here). Lower will cause early death. The diode after Reg 1 is arguably not needed as long as Reg1 is abl;e to tolerate Vbattery on output with power absent )(varies). \$\endgroup\$ – Russell McMahon Apr 8 '15 at 8:34

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