Lindus Embedded

The Android Gingerbread battery service has a JNI interface which supports a power supply class battery driver with hardcoded attributes. However, different platforms drivers may provide different attributes, so to allow for this configurability you can add platform specific system properties like:
devices/<manuf>/<platform>/system.prop

ro.power_supply.ac.online = online
ro.power_supply.usb.online is not supported
ro.power_supply.bat.status = status
ro.power_supply.bat.health is not supported
ro.power_supply.bat.present = present
ro.power_supply.bat.capacity = capacity
ro.power_supply.bat.voltage_now = voltage_avg
ro.power_supply.bat.temperature is not supported
ro.power_supply.bat.technology = technology

And then you retrive and use each of the properties, for example.

property_get("ro.power_supply.ac.online", value, "");
snprintf(path, sizeof(path), "%s/%s/%s", POWER_SUPPLY_PATH, name,value);

For the battery status to be updated by the Battery Service, it needs to receive a uevent from the Linux kernel driver. Verify that your battery driver does something like:

if( bat_status_old != bat_status.status )
    power_supply_changed(&chg_device->psy);
bat_status_old = bat_status.status

At least on the status and capacity update functions.

The battery data is dumped into /data/system/batterystats.bin, a binary file that can be dumped using dumpsys.

Your app would need android.permission.DUMP to execute dumpsys.