HP 49g+ powered from USB

[penguin]

As an owner of an HP 50g+ I learnt some time ago that this calculator can be powered through USB, even when main batteries are removed. It’s a nice feature that can help avoid spending money on batteries.
Recently I bought a second-hand 49g+. It works perfectly with batteries as expected. However, I tried to power it up from USB with main batteries removed like the 50g+ and unfortunately it doesn’t work this way. I wonder if this feature found on HP 50g+ is not available by default in 49g+.
Could anybody please confirm if this is the normal behavior for 49g+ or maybe my calculator has a hardware problem in the power supply circuitry that prevents it from working from USB?
Thanks in advance and excuse my poor English.