A20 Debian won't boot with battery connected

[dipsie]

Hello all,
I'm having troubles in booting an A20-OLinuXino-MICRO with last Debian image.
The system always boots fine when plugged only to AC power adapter, but it will fail almost always on restart when LiPo battery is connected.
The sequence to reproduce the problem is:
- connect LiPo battery (fully charged)
- connect AC power adapter, system will boot
- disconnect AC power adapter, the system is still alive on battery
- issue a shutdown command
- when the system looks like dead (all leds are off), plug the AC adapter again
- the system will try to restart (power_start = 1 in script.fex) - red and green leds are on and the lcd will blink - but it will fail in the middle of the boot process
- press reset button and the system will boot fine as first time

Since I'm developing a kiosk application I can't take out reset button and press it at every blackout...

Is anybody experiencing similar issues or my board has some hardware problems (power supply)? What may be the cause? Kernel? U-boot? Debian?

Thanks,
Alessandro