There is no way to increase the AC output from your standard inverter because there would be no reason to. The output AC voltage should be closer to 120 volts so it appears you have an internal problem with the inverter. A 100 volts AC output from the inverter would indicate a battery voltage of 10 volts DC and since these are new batteries that not likely, but it might be a good idea to check them just to be sure.
2007 Newmar DSDP 4023
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