Lars and Lisa -
In addition to Jerry's comments.
1. Check the water level in the battery. It is possible that the previous owner didn't add water when needed. If the level is really low, and has been for a long time, the battery may very well be ruined.
2. As Jerry said, check the fuses, especially the one that is in line just a few inches from the battery positive post. If this fuse (or the fuseholder) is bad, it completely isolates the battery from everything. It won't charge on the road, it won't charge in the campground, it won't charge at home, and it won't power any TM loads. On the other hand, if the fuse is good, the battery should charge whenever shore power is available, and should charge on the road as you dirve if your tow vehicle is properly set up and you turn the refrig off. Use the Search tool to find discussions on that topic.
3. What year is your used 2720? What is the make and model of the charger/converter? This will tell us whether it has the float capability that Jerry mentioned.
4. If you can't keep shore power on the TM when it is in storage, then you should disconnect the battery. The parasitic loads (plug that term into the Search tool!) will drain the battery in less than a week. To avoid this, many users have installed a battery disconnect switch (use the Search tool there, too!)
Bill
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