My built-in battery monitor - any good?

[breeves2245]

New Passport SL 229 RK. On my first trip. Getting used to all the features. Replaced the 24 grp battery with two Trojan T-105 6 volts. Just bought a Victron Smart Shunt yesterday and will be installing on my next stop.

I was checking my tank levels and noticed for the first time a battery monitor in the system's electrical/switches plate. The one by the front door with all the switches.

Wondering if this is accurate. Guess it doesn't matter since I'm installing the Smart Shunt, but would like to know.

[chuckster57]

Depends on what your definition of accurate is. If you only need a roughy estimate then it’s adequate.

[dutchmensport]

If you are plugged into shore power, the converter on your camper is also charging the battery and monitoring it. When plugged into shore power, that battery indicator on the panel by your door will always read "full". It's only "accurate" if you are not plugged into shore power. But? what exactly does "full", 3/4, 1/2, empty actually mean on a battery?

[flybouy]

Any battery under charge will read the voltage of the charge being applied. As has been stated, that idicator doesn't report an actual voltage but an "interpretation" by the IC chip inside. On our travel trailer I installed a digital weatherproof digital voltmater in the lid of the battery box. The battery is mounted on the tongue so it's convenient. When I turn on the disconnect switch (also mounted through the lid) I immediately know the voltage. That way I can decide if the battery is sufficiantly charged before operating the electric tongue jack.

[MarkEHansen]

Volt meters will register lower voltages based on the load on the battery. There is a chart (which you can find online) which shows what voltage relates to what % charged the battery is, but this only works when the battery is at rest (no load for about an hour or so). This at-rest state is pretty hard to get in an RV, which has stuff drawing from the battery all the time.

Realistically, the best way to monitor the charge on the battery is through the use of a shunt-based battery monitor. I have the Victron 712 smart monitor and love it. You configure it for the capacity of your batteries and it keeps track of Amps in and out and shows you a %charge indication. Very nice.

[snoobler]

Originally Posted by breeves2245

Wondering if this is accurate. Guess it doesn't matter since I'm installing the Smart Shunt, but would like to know.

It's not. Especially if you have to ask. It has limitations and can be useful in certain circumstances, but it's a truly atrocious means of determining charge.

You picked a winner with the smart shunt.

Worth a watch:

https://www.youtube.com/watch?v=4ReljfO3k6M

While it's for the BMV-7XX, the settings are the same.