State of charge

[Bobg]

My 7 year old  t  105 batteries seem to be wearing down..I have a Victron battery monitor that reads soc 100..however with a hydrometer I get 1 or 2 balls floating which means 50 percent of charge..should I trust the monitor? Or the cheap hydrometer..with 5 amp per hour fridge and some led lights after 2 days on the hook..monitor reading around 58 percent ..I need my start battery to start engine..house bank will barely turn over engine...think I need new batteries?

[DaveBMusik]

This has a nice chart with voltage, specific gravity & state of charge

https://www.emarineinc.com/Batteries-Maintenance-101

[Jim Hardesty]

Here is a lot of information on state of charge and specific gravity.
http://www.rolls-battery.com/content/technical-downloads?q=node/51&phpMyAdmin=2eda4dec0bd69647b9e3cf0f71e01d23&phpMyAdmin=9dec4a269d70t7a63be7c

a lot more info
http://www.rolls-battery.com/content/technical-downloads

I'm no battery expert.  But I'm happy to give advice.  With 7 year old batteries you could try equalizing the cells.  Got nothing to loose except a few hours on the boat.  Not so bad.
IMHO  If you are going to measure specific gravity get a good hydrometer.  Out of pvc pipe I made a holder for mine and it's always in the boat.  Gallon Arizona Ice Tea containers make good distilled water containers.
Jim

[Roc]

My charger has the equalizer setting but I never tried it. Is there a certain procedure. Instruction manual doesn't say much.

[Jim Hardesty]

My charger has the equalizer setting but I never tried it. Is there a certain procedure. Instruction manual doesn't say much.

Roc,
My Xantrex instructions work for me.

http://www.xantrex.com/documents/Battery-Chargers/TRUECharge-2/975-0526-01-02_Rev-D(Truecharge2%20Battery%20Charger%20Owners%20Guide).pdf

Hope this helps,
Jim

[KWKloeber]

My charger has the equalizer setting but I never tried it. Is there a certain procedure. Instruction manual doesn't say much.

And that would be...... what charger?

-kk

[Clay Greene]

Maine Sail has many lengthy discussions on his website about how traditional shunt-based battery monitors become less accurate as batteries age.  I would trust the specific gravity readings, particularly given that seven years is a good long lifespan for a flooded battery and what you are experiencing with usage.  But you could also try equalizing them to see if that makes a difference. 

FYI, I had a Victron battery monitor on our first boat but I went with the Balmar Smart Gauge on the basis of Maine Sail's recommendation.  It is supposed to get more accurate with use rather than the opposite with a monitor that measures based on amps.  Seems to work well so far.  You do not get the amp use measurement but I found that had limited utility for my purposes anyway. 

[Roc]

I have the 40 amp Xantrex Truecharge (original model)

[Stu Jackson]

Maine Sail has many lengthy discussions on his website about how traditional shunt-based battery monitors become less accurate as batteries age.

Nope, that's only because the skippers didn't RTFM.

The Electrical Systems 101 topic has a very important discussion called the Gotcha - please read it.  It parallels Maine Sail's discussion.  The SG and BMs are two different TOOLS.  Each has their advantages and disadvantages.  You have to know what tools to use and how to use them.

[mainesail]

My 7 year old  t  105 batteries seem to be wearing down..I have a Victron battery monitor that reads soc 100..however with a hydrometer I get 1 or 2 balls floating which means 50 percent of charge..should I trust the monitor? Or the cheap hydrometer..with 5 amp per hour fridge and some led lights after 2 days on the hook..monitor reading around 58 percent ..I need my start battery to start engine..house bank will barely turn over engine...think I need new batteries?

Unless you have a very, very good grasp of how these devices actually work and how they must be programmed, DO NOT trust your Ah counter for SOC!!

See the link at the bottom for the "why"... Get a better hydrometer or let the batteries rest unloaded and uncharged for at least 24 hours and check voltage.

Maine Sail has many lengthy discussions on his website about how traditional shunt-based battery monitors become less accurate as batteries age.

Nope, that's only because the skippers didn't RTFM.

The Electrical Systems 101 topic has a very important discussion called the Gotcha - please read it.  It parallels Maine Sail's discussion.  The SG and BMs are two different TOOLS.  Each has their advantages and disadvantages.  You have to know what tools to use and how to use them.

The "accuracy" of the Ah counter does not change, though many of the old original Link 8 bit units are experiencing calibration drift at this age and are beyond ready for the dumpster.

The problem is that the batteries are always changing and the owners rarely keep up with Ah capacity testing and reprogramming.

I would bet on this site there is not even one single owner, with an Ah counter, who has performed a proper 20 hour load test (77F battery at a steady 20 hour constant discharge rate to 10.5V) to confirm actual Ah capacity. Without this data there is no way in Satan's den an Ah counter is even going to be close to accurate for SOC.

These devices get lost on SOC accuracy in as little as 1-2 PSOC cycles (partial state of charge), yet this is how we operate our sailboats. I know Stu touts the "gotcha", and it is a part of the problem but a very, very small part of the issues with Ah counters. I suspect Stu has not fully read or comprehended my article to suggest it parallels the "gotcha". If you do read it, and comprehend it, you will see that the "gotcha" is but one small puzzle piece in keeping an Ah counter more accurate...

I would urge everyone with an Ah counter to read the below article, and then read it again, until it begins to make sense. I simplified it as much as I could but still many readers suggest that it takes them a few reads to grasp it all.

Again the "gotcha" is a very small part of the issue with Ah counters. Even if you program around the "gotcha" you're still not even close to remaining accurate if that is all you address..

If you are not doing a yearly or bi-yearly 20 hour capacity test, at a bare minimum, forget using any Ah counter for SOC data.

Keeping Your Ah Counter More Accurate:
http://www.pbase.com/mainecruising/programming_a_battery_monitor




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