I replaced my batteries with AGM's, and got a 3 stage converter (Ultra III) from Randy at BestRCConverters.com to replace my 1 stage parallax in a Safari. The converter works well. I had to send one back because of the fan noise, but the second one works quietly. The fit was slightly off, but I just used two of the four screws, and it fit fine then.
Wiring was not difficult, just took some time. Make sure and disconnect power and battery first!