Why don't batteries equalize on their own?

it's not the battery's fault, it's the wire, and it's resistance.
there is an extensive writeup here http://www.smartgauge.co.uk/batt_con.html
about how this happens.

excerpt: Battery internal resistance = 0.02 Ohms
Interconnecting lead resistance = 0.0015 Ohms per link
Total load on batteries = 100 amps

The bottom battery provides 35.9 amps of this.
The next battery up provides 26.2 amps.
The next battery up provides 20.4 amps.
The top battery provides 17.8 amps.

So the bottom battery provides over twice the current of the top battery.

Ah - I see -

Let's say there were 3 batteries all wired parallel, all the same distance (length of wiring) to each other -- without a load or a charger / solar panel...

Will the cells "equalize" if there was an imbalance of charge / voltage?

Their charges will "Balance".

Equalize is a term used for applying a controlled overcharge to a battery bank, to both :
stir up electrolyte in large batteries, to keep it from stratifying.
insure individual cells in the battery are fully charged.

If you take 24 cells from a 48V battery bank, 1 will always be lower in voltage than the other 23. The mfg process is not perfect, and an EQ cycle insures all cells are fully charged. It's the "poor mans" method of "battery management". In lithium batteries, you need an individual monitor on EACH cell, to acomplish this, as you are not permitted to over charge Li at any time.

Equalizing lead acid batteries is a process designed to de-sulphate the battery plates by carrying out a controlled overcharge.Equalizing the batteries is a tool that can be used to rejuvenate tired batteries or to prevent batteries from becoming tired.

I have below included links to some battery manufacturers instructions about equalization

Well first if there is no load on the batteries, they will balance out the charge. But do not confuse balance with Equalize, they are two different terms.

The proper way to parallel batteries is with a charge buss bar. It is nothing more than two copper buss bars that are used to connect the parallel strings together.

Shouldn't we build solar systems around the batteries then? Rather than trying to get two pre-made systems (battery and PV) to work together? Sounds more expensive and tedious. Charge controllers / BMS, MPPTs ...etc... so expensive!

Let's say we just one to charge one Lithium iron po4 cells (for simplicity sake):

Stats:
V(nominal) ~ 3.2V
Max charge volt: 3.65 (+/-0.05) V
Max current: 80A
Capacity: 16AH

... and a 6x6 monocrystalline cells -

Stats:
Operating voltage: 0.488 v - 0.50 v
Operating current: 7.51 amp - 8.14 amp


Connect 7 PV cells in series to achieve a Vmax of 3.5 witih a current of 8.14 directly to the battery.

Since the PV panel's max voltage is 3.5, and the battery's maximum voltage is 3.65, there's no way to overcharge the battery. The discharge curve drops from 3.65V fairly rapidly and maintains a relatively flat 3.2V, decreasing the wattage harvested from 28.5W (3.65 x 8.14) to (3.2 x 8.14) 26.0W (-10% loss). I think i can live with that. Of course, connect a diode so that the battery won't back flow to the PV cell.

In this example, would I still be able to charge my battery completely and be able to live without an MPPT and not have to worry about overcharging?

OK solarnoob time for a reality check and education.

First question to you is how much do you pay for 1 Kwh from your electric company. Your answer depends on where you live, but the national average is $0.112.

OK you want to stick it to the man, go off grid and do it all yourself and build you a off-grid battery system and rack up the savings right?

Let's say you live in Kanasas City MO. You only want to use 1 Kwh per day to power your dorm room sized fridge to keep the beer and grape jelly cold. So in Kansas City you will need a 750 watt solar panel, a 12 volt 625 AH lead acid battery, and a 80 amp MPPT charge controller.

Solar panel cost $3 per watt x 750 = $2250
80 Amp Charge Controller = $600
12 volt 625 AH battery cost = $1050
Total Cost not including any materials or inverter = $3900 all paid up front in cold hard cash.

To determine how much per Kwh that will cost you, you use 5 year increments because after 5 years you will have to replace the battery at even higher cost. So in 5 years this system will generate 1 Kwh/day x 365 days x 5 years = 1825 Kwh. So the Kwh cost = $3900 / 1825 Kwh = $2.14 per Kwh.

So again how much do you pay the electric company for a Kwh?

Thanks for the insight.

My electric cost per KwH is very average. Then, add on the service delivery fee, "competitive fee" (whatever that means) -- it come out to be a little more expensive.

I used 70 kwh last month, and paid about $30 USD... which comes out to about $0.45 / kwh. Not much, even when compared with the +$2.00 / kwh you quoted me for an off-grid system.

I would like to stress that being "economical" is merely secondary to what the true intentions of building an off-grid system. Sure, it would be nice if an off-grid system cost more around $1.00 / kwh.

Long story short, I come from a family that is extremely frugal and would never waste. My parents, in their elderly state, refuses to turn on the A/C, even when it's +90F outside.

"We don't want to waste electricity"

I thought it would be nice to set up a little system for them to plug in a portable fan / A.C. device powered by solar. There would be no excuse then for "wasting", since they'll be making the power themselves. Of course, the money creating the system far exceeds the cost of the power itself, but it's just their mindset.

So, I'm trying to create something that may bring down the cost of an off-grid system..... As you can see by my previous question, i'm trying to rid myself of the MPPT charger / BMS.

If not today, or this year, someone in the near future will be able to create just that product. And that someone might just be one of you folks.

So again...

I understand but you need to be clear, or at least honest with yourself what the primary reason is. If you are thinking along the lines of earth friendly or frugal you need to know that with a battery off-grid system is neither earth friendly or conservative. The reason is battery systems are very inefficient and at best are only 50% if you could possible use all the energy that it produces which is almost impossible. They are negative EROI, meaning it takes more energy to manufacture the components, than the system will ever produce.

This is the very reason I and other professionals say off grid battery systems should only be used where there is no feasible commercial power available. Something like a remote cabin, or what I do building remote cell tower sites in the desert southwest.

You can' without destroying the batteries. Solar panels are passive dumb devices and cannot regulate power. You hvae to have a regulator in between th epanels and batteries. A BMS is not needed unless you use Lithium batteries, even then is not required. The reason for a BMS is straight forward, Lithium batteries are 10 to 30 times more expensive than lead acid batteries and you want to protect that investment. BMS systems are more in the realm of electric vehicles that have thousands of lithium cells.