Found this on the web while looking for an alarm for our house batteries. The idea is that when the house batteries read a certain voltage (we set it at 12.00 volts) it is supposed to sound an alarm alerting us that we need to turn the gennys on to recharge. It is called
Voltminder. We wired it up today and will be boondocking this weekend so will give a report. If you decide to get one, let the guy (a one man shop) know that we posted this info; we're always trying to help another get ahead if the product is worthwhile.