Same thing happened to a guy in a Toyota van during the week. Worked well for a couple of hours. The next time he tried the heater (meant to be a Chinese copy of a Planar) it pumped out an amazing amount of smoke, and appeared (smelt) to be flooding. As you say a low battery could be the problem.
I'm undecided; try a cheapie or shell out $1400 for a German brand
We have a 2kW Webasto in our caravan. Has done over 10 years of service without missing a beat (and it does not blow smoke or smell). This year we noticed that the heated air stream was not quite as hot as we remembered - booked it in for a service - back to being as new. I do not have any experience with the cheaper options but can certainly vouch for the brand name version (was one of the first installations in Australia and cost about $2000 installed 11 years ago - was the only SIDS approved free camping heating option for our caravan)