Batteries in Parallel

[drtrott]

I bought a used 2004 Laredo that needs some work. I replaced both batteries with Costco 27's and wired them as previously done, in parallel. The batteries would not work. I had power to everything when on shore power or when connected to the tow truck, but nothing when standing alone. A volt meter said I was getting about 12.75 volts for each battery. When I disconnected one of the batteries completely. I get power on stand alone from the other battery. Any ideas what is going one?

[Roller4Tan]

If you're connecting pos to pos and neg to neg, it should work, unless it's tripping a 12V breaker up stream somewhere, or the wire from the last battery to the fuse panel has an open.