I had put this project off because I wanted to upgrade my RV's control console. Finally, I got around to designing a new console, which gave room for this battery monitor.

I had originally considered one of those inexpensive eBay/Amazon/Shenzhen Marketplace DC monitors, but decided I wanted a more comprehensive monitor as the cheap ones had their limitations.

I had an eye out for both this monitor as well as the Xantrex LinkLite monitor, but opted for this one after discovering it had an optional BlueTooth interface.

This monitor is available in several versions, depending on your needs.

• BMV-700 - basic monitor (bluetooth capable with optional dongle).
• BMV-700H - high voltage version (bluetooth capable with optional dongle).
• BMV-702 - dual battery monitoring capable, plus temperature monitoring (bluetooth capable with optional dongle).
• BMV702B - Black version (bluetooth capable with optional dongle).
• BMV-702 Combo - Monitor (includes bluetooth capability).

Since I only have one battery in my RV, I went with the BMV-700 plus bluetooth dongle. Total cost was just under $200.

The above charts should the major differences between 5 popular battery monitors. For example, if you only have one battery, need the ability to start a generator when the battery voltage goes too low, need Bluetooth connectivity or other characteristic - you can easily determine which monitor would work best for you.

Note: I could not determine if the Xantrex monitors require the connection kit or this is an optional longer distance kit.

Installation consisted of locating the shunt as close to the battery as possible (18" of cable or less), then running the monitor cable to the display unit location. Of course, this will most certainly require some "fishing" the monitor connection cable through the RV, and a bit of drilling and cutting.

The Amp Hour (20 hr rate) capacity of your battery is required to accurately determine the remaining capacity in the battery. More accuracy can be obtained if you can find the Peukert exponent, but often this factor is not available. If you cannot determine the AH rating, use the following:

What is the 20Hr rating? The Amp Hr rating is determined by discharging a battery at a certain amperage for 20Hrs. For example, a 100AH battery would be tested by discharging it at a 5Amp rate (5A x 20Hrs = 100AH). Can you use another hour rating? No, due to Peukert's Law, which basically states the AH rating differs at different discharge rates.

For example:

Discharging a battery at 5Amps gives you 20hr of service according to the above formula. But a higher discharge rate of 20A does not give you 5Hr of service - it is less.

When you discharge a battery at higher rates, internal heating and other factors reduces the AmpHr capacity - that is Peukert's Law in principle. So if the AH rating of your battery does not specify a 20Hr rate, then is most certainly different.

A good example of this is trying to start your car on a cold morning with a old battery. Have you ever cranked the engine until the battery can no longer turn the starter... but then try again 15 minutes later and it starts? This is an example of Peukert's Law in a real situation. When initally attempting to start the engine, the battery heats up, so less than 100% of the battery capacity is available. But after resting, the battery cools down, then the remaining battery capacity is available.

Note however that at lower discharge rates, Peukert's Law has less effect. But to obtain the most accurate capacity readings, both AH @20Hr and the Peukert's exponent must be known. The battery monitor uses a default of 1.25 for the Peukert exponent if not known. This provides a reasonable accuracy.

There is a really good - if somewhat technical - explaination of Peukert's Law in the BMV-7XX manual.

Installation Notes:

• Purchase pre-made #4 battery cable 18" or less.
• GenuineDealz will make a custom 4AWG cable for you for less than $10 (you don't need a hydraulic crimper).
• The Shunt requires #12 mounting screws or 3/16 Carriage Bolts (hard to find).
• Batteries may have either 5/16 or 3/8 terminals. The shunt uses 3/8 terminals.
• The Bluetooth instructions are not in the BMV manual, but on Victron's website.
• Default paring code is "000000". You can change it if needed (recommended by manufacturer).
• Contact the battery mfg for the AmpHr capacity (20 hr rate) for your battery and Peukert's exponent if available.
• The AH capacity for my Deka (East Penn Mfg) Group 27 Deep-Cycle battery was 90AH.
• Keep a spare 5x20mm 100mA fuse in your spare parts kit. They may be hard to find locally.

While this page may seem brief, I encourage you to consult the manual (you can find it as a .pdf on-line if you want to look at it before purchase). There is no reason to replicate that information, so I am providing the installation notes that may be helpful.