Let's say I have a battery with V volts. A conductive material (Material A) is connected only to the battery's positive terminal. Material A is then connected to a second conductive material (Material B) that is not connected to anything. After Material A and Material B touch, they will then be separated. How do I calculate the charge on Material B after the two were separated?
Electronic – Calculating induced charge
charge
Related Solutions
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)
Ignoring charging losses (and I'll get to that), the first statement is wrong and the second statement is correct.
Converter efficiency is measured in terms of power, not current. So, for instance, a 12-volt input at 1 amp would give a 4-volt output at 3 amps, and that's why the 75% figure is correct - it is 3 times greater than the first.
With that said, even if you have a perfect converter, batteries do not charge with perfect efficiency. At the very least, they start getting hot towards the end of the charge cycle. Even when charged, a battery's capacity has to be measured by a discharge cycle, so charging efficiency is actually efficiency through a charge/discharge cycle. Wikipedia suggests a charge efficiency for li-ion batteries of 80-90%. A standard 16-hour @ 0.1C charge cycle for NiCads produced a maximum efficiency of 62%.
Best Answer
Charge (Q) is the product of current (I) and time (t).
When you connect something to one side of a battery only, no current will flow, and no charge will be transferred, except for extremely tiny amounts of charge when you consider your conductive parts as plates of capacitors.
There are some experiments with high voltage that work a bit like what you mention in your question. At high voltages, charge transfer can even be observed in the form of tiny sparks.
However, without knowing how big your setup is, and what (stray) capacitance to use, it is nearly impossible to calculate anything.