Lead Acid Batteries are used widely in Caravans, Motor-homes and Camper-vans for providing power to 12 V appliances. They can last many years as long as they are not discharged below 50% too often. Monitoring the battery voltage is a good way of keeping an eye on the State of Charge (SOC) of the battery. At normal temperatures (15 to 25 deg C) one would stop discharging the battery below 12 V - at which voltage the typical Lead Acid Battery is at 50% capacity.
 
This Battery Monitor Buzzer starts beeping as the battery voltage drops down to less than 50% and then with increasing persistence as the battery voltage drops down even further - it is hard to ignore. 
 
The cost of this unit is easily recovered in extending the life of your 12 V Lead Acid Batteries from 1 or 2 years to 6 or 7 years.

It can also be connected to a bank of parallel 12 V batteries as used in renewable energy systems.
The Battery Monitor Buzzer also has a user calibration function to adjust it to different types of Lead Acid Batteries and also for operation at different temperatures as this can change the relationship between battery voltage and State of Charge (capacity).
 
This unit is Made in Yorkshire and uses high precision components to measure the voltage accurately - unlike many cheap imported devices that are mass produced. It is supplied with user instructions and technical support is just an e-mail away.
 
The Battery Monitor Buzzer is supplied in a plastic enclosure. The user has to just connect the wires to the battery +ve and -ve terminals. Product size: Length = 70 mm  Width = 50 mm  Height = 25 mm
 
Please note: This device is not for use with Lithium Batteries as they have a different relationship between voltage and capacity. It should not be connected across a 24 V battery bank.