I remember that for the HTC Tornado there was a setting to disable USB charging - to allow the battery to continue discharging while connected via USB (useful or not is another topic - see further down). As long as the device is switched on, the USB and Battery drivers of the Windows Mobile operating system have control of the charging functions. When switched off, the "hardwired" functionality of the BootROM code takes over. The following only affects the options while the OS is active.
My search in the extracted modules for registry options has revealed in the usbotg.dll the elements:
As written further down, my (refurbished) device was delivered with a non BenQ charger (a Blackberry with exchangeable plugs) - so I continue to use my old HTC Tornado charger which also connects via miniUSB. The systematic (lengthy) investigation has shown the following logic for the registry variables above:
- none present: device charges from any source (just like when switched off)
- Charging via USB connection cannot be disabled without also disabling the HTC AC Adapter (USBForceCharge = 0 disables both), but
- charging via HTC AC Adapter can be disabled, still with USB charging possible (set USBChargeEnable = 1; if you want it the other way round - it will not work, I have tried all options)
- Charging via Blackberry AC Adapter can be configured independently of the USB Charging (and follows an understandable logic), I suspect the same will also apply for the normal BenQ/Kyocera AC Adapter.
- ACCurrent = 0 disables the charge via the (BB) AC-Adapter
- USBCurrent = 0 disables the charge via the USB cable of the linked PC
Now the question "is it useful to discharge the battery (completely) before charging again"? After consulting many resources around the web I strongly believe "no". When busy with the batterylevel problems of the device I have collected some links - make your own decision, see here: 1, 2, 3
I know that some are keen to get hold of the Flash animated homescreen that is present in the Asian ROMs (and I suspect that most parts can be extracted from an available - yet incomplete - dump) but mind that everything that happens automatically on your device will need the CPU and battery. So I recommend reading this article at wmexperts.com.
After running down the battery completly, I have discovered that the charging current (get it from HKLM\System\State\Battery "ChargingCurrent" value while charging) is limited to roughly 450mA when connected via USB (also for the HTC Charger) - the USB standards allows a maximum of only 500mA anyhow. When connected to an AC Adapter (that is recognized by the system as such - e.g. my Blackberry AC Adapter) then the current draw is higher - I have seen 650mA when the battery was recovering from "emergency switch off".
The lowest voltage until which the battery is used in the E72 is very low compared to my HTC. The E72 uses the battery down to 3.356 V, while the HTC switches off already at 3.570. This may sound like big difference, but it is not in terms of capacity when you look at the discharge curve for LiIon rechargeable batteries. The battery resources I have seen on the web (see links further up) usually recommend not to use a battery below 3.6V to preserve a good lifetime.