Inexpensive Battery Monitor?

[JVM225]

I'm looking for some ideas for a simple, inexpensive battery monitor for when I'm out on the hook.
My boat does not have a genny. I have two batteries on the starboard motor that also feed everything 1 volt on the boat. There is one battery on the port motor dedicated to that motor and nothing else.
I generally select only one of the starboard side batteries after I drop the hook so as not to run down both of them running things. So far it has worked ell for me, but I thought it might be nice to be able to see how much I'm drawing and how much I have left in the battery.
Anyone have any ideas?

 

[alien1952]

You could install SPDT or DPDT switch in the dash to switch from main system battery to the aux battery
Dash voltmeter is powered by a purple wire. remove it and extend it to the top terminal of the switch,
wire from the switch to the gauge for "up " for the main engine system and "down" to monitor the second battery`s voltage.

 

[mixman]

I suppose it depends on what you mean by "inexpensive". I've had a Xantrex LinkPro for years. I think the $265-ish price is well worth it. There's a lesser model, LinkLite, for closer to $200. Both need a DC Shunt installed (included). BillyIII loves the BalMar Smartgauge (no shunt needed). It runs closer to $320. In the long run they do have a decent ROI considering they can help you extend the life of your batteries.

 

[Radioactive]

There are several things that a person might wish to know about their boat's electrical system.

Voltage. While it can give some indication of "normal" vs "abnormal" operation,, unfortunately simply measuring voltage gives little useful information.

Current. Knowing the instantaneous current flow can give you more useful information than voltage, in practice, it only allows you to control the load ( ie: things that are ON ). Average current flow over time period is more useful, and cumulative current is also a plus. But, again, you are measuring the beginning and end, but ignoring the middle ( ie: the battery )

Actual measured battery system charge state. ( ie: Smartgauge ) The method is proprietary, but appears to be actual testing of the battery which gives the actual charge state of the battery. Combined with battery performance models, this should give an accurate view of the present status of charge available for use. This is a VERY useful number.

If budget allowed, I would use a Smartgauge plus a mid- to upper- range current monitor. This would allow not only the load to be measured and controlled, by would allow control of charging as well as providing an accurate state of charge. ( ie: fuel gauge for your battery ). Voltage is purely optional and, for me, mostly useless.

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I know of no "cheap" current monitors or charge state monitors. So, if you went with what I would "like", you would spend in the neighborhood of $600 for what I have described. This may or may not be "inexpensive". Depends on your budget and need.

 

[Sandy]

Billy III posted about a Balmar Smart Gauge monitor he was really impressed with back in April:

http://www.boatered.com/forum/topic.asp?TOPIC_ID=165374

It requires no shunt, but cost is over $300 so this may not be the inexpensive device you seek.

Do you just want a cheap digital voltmeter, or a monitor that keeps track of charge and discharge flow to monitor remaining capacity?

If just voltage , a quick search shows something called an Xscorpian 3 digital voltmeter for under $12 . You could get one for each battery or a switch to toggle between multiple batteries. I expect there are many similar voltmeters.