The Volt Minder 12 Volt Battery Alarm from Universal Power gives a digital readout of battery voltage, and has a settable battery voltage audible alarm. This can prevent starting issues, and battery damage from over-discharge conditions. The readout can also be used to verify battery charger or alternator function. These come with lighter plug adapters installed, but could be hardwired if desired. They have an illuminated LCD, for easy nighttime viewing. The lighted LCD display is a neglibible milliamp draw. There are numerous inexpensive digital meters around, most of which are inaccurate up to a couple of tenths, which is huge in battery management. These are among the most accurate we found, down to the hundredths of a volt. These are mountable, or can be used as a portable meter, and are excellent for industrial equipment or any 12 volt battery, or battery system. Part 71730.
UPG 12 Volt
|Box Dim (LxWxH):||4.125 x 2.75 x 1.0||Mountable|
|Actual Weight:||.5||Digital Display|
|Ship Weight:||2.0||Adjustable audible alarm|
|Range:||To 19.99 VDC||Lighter plug adapter|
|Alarm Range:||10.5 to 13.5 VDC||Mounting kit|
A lot can be determined by knowing a DC system voltage, both at rest, and when being charged. This requires an accurate digital volt meter, at least to the tenth of a volt. You would think in this digital age that any digital device, particularly a meter, would be so. This is not the case. The Universal Power Group Volt Minder digital meters are accurate. Knowing that a 12 volt lead acid (or sealed lead acid) battery is fully charged at 12.7 to 12.8 volts (depending on the battery construction), and is effectively discharged at about 11.9 to 12.0 volts, the state of charge can be determined by an accurate voltage reading to the tenth of a volt, and comparing to known values. If you have a 12 volt battery that never reads above 12.5 or 12.6, after a charge cycle and resting period (about 12 hours), you have a battery with diminished capacity, and is either on the verge of failure due to age (chemically worn out), or is sulfated enough to cause the capacity problem. Sulfation we can deal with. Chemically worn out is worn out, and unreliable. Maximum battery life is accomplished by minimizing time spent in a partially discharged state (like a golf cart left unmaintained over the winter).
As for battery charger function, remember, chargers work by forcing energy into a battery and exceeding its resting voltage. So, if you put 11 volts to a battery that is sitting at 12.1 volts, no transfer of energy (charging) occurs. Generally, 12 volt battery chargers will go up to 14.2 to 14.8 volts in the final stage of charging, to cram that last little bit in and fully charge the battery. Going too high can damage the battery. If you get a voltage reading from your digital meter, and then turn on the battery charger, the voltage should start rising. It may take some time with a large battery/small charger combo. If you never get a voltage rise, the charger is not working properly (we assume you have a viable battery, because it registers on the meter). If you monitor the volt meter, you should see the voltage rise to the 'absorption' voltage setting of the charger, then drop either to the 'float' voltage setting in the mid 13 volt range, or slowly drop to the 12.7 or 12.8 fully charged battery range because the charger has shut off. This is useful information to have available.