Yep it's a battery low voltage alarm, though when we had the Panda the bloody thing went of in the middle of the night while we we're using the van yep asleep didn't know what the hell it was, it was quite loud, couldn't figure out how to stop it funny thing though, we we're on main power, it then off again packing up next morning after I disconnected the power from van, never did find out what caused it, and never happen again, was later told the best thing for Topray controllers was to chuck them in the bin.
Current van has topray hasn't been a problem, though it's mounted in the boot, though when we got thrown into darkness a few weeks ago while away, I discovered the charger had been turned off ,things we're running on 12v but hadn't had enough sun for solar to keep up in this case the alarm was very faint and couldn't be heard.