Electronic – –Electric Bike— How to measure left percent of battery

The discharge rate dependes of several factors and will vary from manufacturer to manufacturer.

A good Li-Poly typically has 2-5% self-discharge rate per month. If it has a PCM (protection circuit module), that module will draw some current, expect less than 1uA for such a tiny cell. Parts of lesser quality may draw 30uA or more.

Self-discharge increases with temperature. I believe it also varies with cell construction (cylinder, prismatic etc.) Quality varies a lot from manufacturer to manufacturer so you have to ask for the exact specs.

UPDATE

I don't have much experience working with the current levels you mention. Wouldn't the ground current in the charger consume most of the 10-20uA? There is a lot of interest in energy harvesting and someone else can probably give a better answer. Slow-charging the battery is OK provided you cut off at 4.2V. My guess is that 10-20uA is not enough to offset self-discharge and other losses, but I'm frequently wrong.

There are a couple of things you can do to cut down on the transmission rate.

1. Only transmit when you have moved more than a certain distance... eg, 50ft or so.

2. Cut down on the transmission size.. 1 second seems like a long time for an I am here packet. 40mS seems more in the ball park.

3. Use adaptive transmission based on available power. i.e reduce transit rate when dark and have not moved in a while.

From a sanity check, something also seems off with your math.

If it's 12V and max current is when it transmits at about 0.5A, that's only 6W if you are transmitting 24-7. At one second every five, that's just over a watt. From that alone, a 225W solar panel would be serious overkill even if you do want to charge a battery so it works for a few days in a garage.