Trojan T105 Charging Efficiency

[john61ct]

That's not long for a quality bank, depending of course what SoH you define as EoL.

Coddled may have lasted double that.

[Pizzazz]

John, those golf cart batteries were purchased in 2012 for 69.99 a piece. I do not know if it can get cheaper than that. I am sure better quality batteries exist but you can't beat that price performance. I was ready to replace them in 2014 . I replaced them since they would not hold charge as before and the voltage drop under moderate load was excessive. Also, the batteries looked physically deformed, buldging in the middle. Equalization stopped being effective months ago.

[john61ct]

As I said, determining EoL can be tricky, industry standard os when SoH has dropped to 80%.

70% is pushing it for those avoiding "sudden unexpected" failures.

Deformed case is way past, risking dangerously destructive events.

[sailorboy1]

Originally Posted by sailorboy1

90% seems to be working well with the combination of half bulk charging via generator/battery charger and half slower solar bulk/absorption charging. My gut feeling is that with full solar slower charging only you could probably use a higher efficiency.

So after 6 months of watching how the SOC reading tracks with battery amp acceptance on my battery monitor, the 90% Charge Efficiency setting on the battery monitor appears to be as close to correct as possible.

It seems to hit the 0 amp-hour out/100% SOC point a little early if I motor all day and the battery is getting supplied by my alternator, but I would say the battery was at 99% charger based on the acceptance.

If the solar is getting it near fully charger the battery slowly climbs to absorption voltage and gets there right at about a reading of 98% SOC and -7 AH out. Right about the point that the unit reads 100% SOC and is 0 AH out the battery acceptance is down to around 0.5%C.

[billknny]

Originally Posted by StuM

Charge efficiency = amp hours stored per amp hour input

Maybe, and then again maybe not...

Charge efficiency numbers are confusing because there are two very different ways to talk about it, and people frequently don't know that they are talking about different things.

Because also TRUE is:

Charge efficiency - Watt-hour stored per Watt-hour input

But these are very different numbers. Battery makers usually talk about the Watt-hour efficiency of their batteries, because it is the technical measure that actually matters.

Because boat owners monitor their batteries with amp-hour meters, we talk about the Amp-hour efficiency.

For a typical FLA battery the Watt-hour charge efficiency is ~80-83%. The same battery can have an Amp-hour efficiency of 95-98%--or even higher. 80% for an amp hour efficiency is very, very low. That would mean that about 40% of the generated power is lost as heat. I charge my 24V battery back with 170 amp during bulk charging. If 40% of the power was lost as heat that would mean my batteries would be functioning as a 4000 Watt heater... I KNOW that is not true.

Why the difference that nobody seems to know about? Because one amp of charge current at 14.4 Volts contains a great deal more energy (Watts) than one amp of withdrawn power at 12.6 Volts.

For my AGM battery bank a number of 102% for AMP HOUR charge efficiency worked in my setup.

[travellerw]

Originally Posted by Pizzazz

John, those golf cart batteries were purchased in 2012 for 69.99 a piece. I do not know if it can get cheaper than that. I am sure better quality batteries exist but you can't beat that price performance. I was ready to replace them in 2014 . I replaced them since they would not hold charge as before and the voltage drop under moderate load was excessive. Also, the batteries looked physically deformed, buldging in the middle. Equalization stopped being effective months ago.

Thats a pretty good life for CG2s. Down here, most people get about 3 years of service out of a CG2 set. Of course there is lots of factors and some people get longer, or less, but most budget for 3 years.

Our CG2 bank is just coming up on 3 years old and based on the numbers today, I would have expected another 1 - 1.5 years out of it. However we are in the process of changing to LiFePO4 so I won't get to see that. I'm hoping to pass them on to another cruiser to see how long they last.

I also agree that they are an excellent value. Pretty tough to beat at $70-$80/battery.

[SV THIRD DAY]

One would think that Someone with 13k posts should know how it works...you ask Question A and get answers and commentary on B-Z. Usually because Question A can't really be answered as a stand alone.

[john61ct]

Takeaway for me is that 90% number is correct for that bank at that age with those usage patterns.

That number in itself is more or less useless for other members.

But the resulting discussion educated hundreds on the all-important **process**

which is very valuable stuff.

So thanks to all!

[sailorboy1]

All I wanted to do was post a real life 6 month proven answer in case someone decides to try the search feature. I am of course as always, wrong and an idiot

[john61ct]

Chill dude, no one said anything like that.

In fact I explicitly thanked you for stimulating the discussion.

[rgleason]

Originally Posted by sailorboy1

All I wanted to do was post a real life 6 month proven answer in case someone decides to try the search feature. I am of course as always, wrong and an idiot

Sailorboy, many thanks for your persistence and posts. It is a helpful example.