Newbie Battery Bank Depletion

Patriot65 · August 2019

Totally new to this, I have four Battle Born 100amp 12 volt batteries in parallel with a Victron battery smart monitor, and I am getting nowhere near 4800 AH. The voltage drops too quickly under load, after 280 AH the voltage dropped to 11.6. Even with the voltage continuing to drop the Victron monitor said I still had 99%. The battery bank seems to charge too quickly as well, (400 watts of panels, max current 20 amps today). I assumed I could draw 75% of 4800 AH without a significant voltage drop. Is my math correct?

BB. · August 2019

Welcome to the forum P65,

I think we are having some unit name issues.

200 AH is the capacity of the bank in Amp*Hours.

The capacity in Watt*Hours is

200 AH * 12 volts = 4,800 WH

That is a complete unit. {If you know amps and ah, you need to know the working voltage}.

So, you should be able to draw upward of 75% of 4,800 WH.

Or 75% of 200 AH... Depends on what units you are using.

You average solar harvest is something like

400 Watts * 61% off grid system eff * 5 hours of sun = 1,220 wh per day

1,220 wh / 12 volts = 102 ah per day

There are lots of details, but the above is roughly correct estimate for a well working system.

Bill

Photowhit · August 2019

I'm puzzled by your system as well, appears you have;

Patriot65 said:

four Battle Born 100amp 12 volt batteries in parallel

So a 400 amp 12 volt battery bank, or amps x volts = watts, 4800 watt hour battery bank? Correct?

Patriot65 said:

The voltage drops too quickly under load, after 280 AH the voltage dropped to 11.6.

So here you appear to be describing a load. Is it 280 ah 12 volts? Could you tell us more about the load and how it is wired to the battery bank?

Patriot65 said:

Even with the voltage continuing to drop the Victron monitor said I still had 99%.

So which battery monitor? A shunt based monitor? What information did you give it? Perhaps does the monitor think you have a 4800 ah battery bank?

Patriot65 said:

The battery bank seems to charge too quickly as well,...

How are you assessing this?

Patriot65 said:

(400 watts of panels, max current 20 amps today).

Don't know where you are located, but that seems about the correct max from 400 watts of panels into a 12 volt bank, perhaps a little more might be expected, but not much.

Patriot65 said:

I assumed I could draw 75% of 4800 AH without a significant voltage drop.

Being able to use about 75% of the capacity without a large voltage drop, should be correct for lithium batteries if fully charged. Many people suggest only charging to 90% to extend battery life and perhaps you have setup your charge controller to do so?

So about 3600 watts hours, If you had set your charging to 90% and used 280 ah, I would think you would be seeing the knee of the curve. There may be other bits of load that haven't been told, wire size to the load and voltage drop across the wire, the size of the load to help assess the voltage drop. If an inverter was used, did you take into account the energy lose/used by the inverter?

Newbie Battery Bank Depletion

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