On 07/29/2011 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.

> Hook-up: -brand new yellow top battery

Over-rated battery but people like them.

> -Stock attachement to the starting battery (had to replace the
> relay)

Okay.

> -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).

Nothing unusual there.

> -Inverter is a 375 watt Tripp-lite (good reviews on amazon).

And you said you got same or similar results with another inverter.

>> -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

What's the voltage at the battery with the car not running and no
inverter attached?

> -All the inverters I saw shut off at a little over 10 Volts....

Yup, s'posed to.

There is no way a 375 watt inverter can suck a healthy battery down to 8
volts unless the battery is sick.

So here's my guess: If you see normal charging voltage of 13.6 volts on
the aux battery with the engine running and the inverter connected, but
it sags quickly and heads towards 8 volts once you turn off the engine
with the inverter still attached, then the yellowtop is a goner. Can't
hold a charge.

-- RJS