Need confirmation on diagnosis of 12V electrical problem

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(mods pls move if this is posted in the wrong location)

A friend has a trailer he just bought.

5 days ago when we picked it up everything worked - lights, A/C, fridge, stove, heat, water heater, etc. I towed it over to his house and dropped it off.

Yesterday he had some time to go out and check out the new toy he had bought, so he plugged in the 110V shore line to a 20a 110V plug in his garage (and yes, it was 110V outlet not 220). The the clock on the microwave came on, but no lights in the trailer. A quick check found the following - no 12V.

Pulled the 50A fuse that was in line w/ the battery and the battery only had 0.3 volts. 50A fuse was good. Checked all breakers and fuses and none were open/blown/tripped. Leaving the battery disconnected and connecting the 110V (so the converter would have power), still had 0V on the 12V line.

There is a Parallax Power inverter (http://www.spectrum-x.com/PPS/Products/Converters/PowerCenter/7100/7155/) model 7155 inverter in the trailer. This inverter is in a box that holds your breakers and fuses, along w/ the inverter. I disconnected the blue wire that supplies the 12v and goes from the inverter itself to the fuse panel and reconnected the 110V. At that time I was able to get 4 volts out of the inverter. Re-connecting the line and the output would go back to 0v

I suspect the inverter itself has failed. I can get a replacement for just the inverter from Amazon (http://www.amazon.com/Parallax-Power-081-7155-000-Replacement-Section/dp/B002SSEWD8) but before I blow $160, I would like to make sure I have not missed anything.

I know I will have to get a new battery. My best guess is the output transistor(s) on the inverter shorted/failed after we picked up the trailer (or maybe they were already toasted before we picked it up and the battery was supplying the 12v during out inspection - the prior owner did have the battery disconnected before we started our inspection) and leaving the battery connected for a few days to a failed inverter (with the loads from the CO and methane detector) killed the battery.

Has anyone experienced something like this and was able to fix it without spending $160?

Thx!!!

[Dakota98]

First off, I believe you have confused yourself somewhat with terminology. You have a Converter, not an Inverter.

If I'm not mistaken, some older Converters will not provide 12 volt unless there is a functioning battery connected. I believe your battery is dead.

Most folks here on the Forum will recommend replacing the Converter with a Progressive Dynamics with Wizard, even if your current Converter is OK.

[midnightsadie]

I,ve had that old outdated converter ,change it out easy to do, I ,ll go out to the shop and get the number for the one I put in, can,t remember the name.don,t know about the other problems but you need a good 12v battery to start ,the converter doesn,t do everything ny itself/