A bad battery would be my guess, take it back to where you got it and
show them. My 400w inverter works well off my house battery (it's the
same type/size as my start battery) but I only use it when I have
some that has to have 120v. My advice would be to get a 12v power
source to plug into the battery cigg plug, that's what I'm running my
computer & charging my phone with right now.

Rob

At  7/29/2011 02:17 PM,Daniel Rotblatt wrote:
>Well, I just got back from a trip to Mammoth Lakes (separate post on
>that) and got a chance to try out the aux battery and inverter I
>got.  The problem I had was that with the car off, the inverter
>didn't get enough power to work.  When hooked up (and I tried two
>inverters and got the same results), the voltage would drop from
>12.6 to about 8.x volts - not enough to run the inverter and it
>would automatically shut off.  Thus, the only time I could charge
>the computers (keeping the kids happy), etc., was when the car was
>running.  Is this how it works?  What is the need for a aux battery,
>i could have just hooked up the inverter to the main battery and not
>used it when the car wasn't going an saved $175 on the aux battery.
>
>Hook-up:
>-brand new yellow top battery
>-Stock attachement to the starting battery (had to replace the relay)
>-Inverter hooked directly to the terminals of the yellow top - about
>4' of wire, (I tried just 8 gauge with about 3' of wire, and finally
>with 3' of 8 gauge and a few feet of 12 gauge hooked to that with a
>cigarette plug since that's what was on the inverter).
>-Inverter is a 375 watt Tripp-lite (good reviews on amazon).
>-Voltage at the battery (when new) was ~12.7 , with car running it's
>~13.6, with car not running and inverter attached it's ~8.5
>-All the inverters I saw shut off at a little over 10 Volts....
>
>So...is that what's supposed to happen or is something not
>right?  I'm planning a trip to New Mexico next week, so it would be
>nice to have it working.
>
>
>Dan
>Los Angeles, CA
>'85 Westy Weekender