Quote:
Originally Posted by aha
Are laptops just wired with two separate paths for battery and AC power supply while things like ereaders have a single path that has to go through the battery? If so what's the reason for that design, and is it relatively simple to rewire an old device to run off an external power source?
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Laptops vary. They are mostly designed to still work off external power while the battery is flat. Some have complex controllers that measure each cell in the pack. They tend to use two to eight cells.
Ereaders, tablets and phones usually have a single cell. There are several ways the cell is used. A digital camera might be similar or use two cells.
1. A direct cell and a 3rd wire is a temperature sensor. There is more than one model of sensor.
2. A cell with a built in controller and 1 or 2 wires of serial data.
3. A cell with a built in controller / manager that has only power connections.
There are ereaders that work with a dead cell and external power. The K3 cell has a 3rd connection, but I forget if it's data or temperature. The K3 seems a bit odd.
Generally types 1 & 2 need exact replacement cells, especially 2. Some type 2 also have a battery / cell ID that tells the device what capacity the cell is. Some third party cells will then only work in an external charger and capacity isn't recognised either (common with digital cameras).
Type 3 device will work with any similar capacity and chemistry of cell that physically fits the case. Possibly even a larger capacity, but it depends on the main board.
The nearly flat voltage is about 3.6V and fully charged about 4.2V, but unlike Lead Acid (all kinds), NiCd, NiMH and Silver rechargeable cells the voltage limits vary with exact chemistry / make and temperature. The Cell goes on fire if overcharged. Unlike anything else except LiFePO4, it can't at all be left on trickle charge! That sets it on fire.
Attempting to charge a completely dead, or even nearly dead LiPoly cell may set it on fire, so when a cell gets poor the main board charge controller may not charge it. Decent built in controllers or main board on dumb cells that have only a temperature sensor (often a thermistor, but a special diode is possible) will disconnect a cell when the voltage is too low and disconnect charger when the cell is charged.
Total cycles and temperature and time since made set cell expiry. Ten 10% discharges and charges or 2x 50% discharges = 1 cycle.
Storage is best between 33% and 66%, but unfortunately all the older Kindles have no "off", just a pretend blank screen mode and thus only really turn off when cell has only a few % capacity. Thus older Kindles wear out the battery even if unused in a drawer, but most other makes have a real or very nearly real off, so cell has some usable charge maybe after a year in the drawer.
If I get another cell for the K3, I will fit a real on/off switch as a "battery saver".