Voltage drop from inverter load (large load)

For a flooded cell lead acid battery bank with 2x 12 volt @ 180 AH or 12 volts @ 360 AH bank.... Suggest the maximum continuous load would be around (basically 250 Watt AC inverter max capacity per 100 AH @ 12 volt battery bank):

• 250 Watt AC inverter capacity * 360 AH * 1/100 AH = 900 Watts

So--A 2,000 Watt inverter is "over-sized" for this battery bank--Pulling 900 Watts should be OK from a full charged/well maintained battery bank.

At this point--I think you may be having "battery issues" (assuming you have short/heavy cabling, use bolted clamps and not "alligator clamps"--And you are measuring voltage at the battery bank terminals and seeing the voltage "diving" at those terminals. (and you it does work "better" with 500 Watts of solar input)

First question, did these batteries set on the shelf for >1 month without charging (early sulfation of batteries--Loss of capacity)

Second question, what is the charging voltage you are seeing (and charger set point) for charging... Nominally, 14.4 volts or so and once 14.4 volts is reached, hold for 2-6+ hours to fully recharge (shallow discharge ~2 hours... Deeply discharged ~6 hours absorb time).

Not a deeply technical "manual" for Varta--But some details on charging (I think yours is flooded cell type). Note: Our "standard" for for recharging Lead Acid batteries is to recharge if 75% or lower state of charge (to prevent rapid sulfation during non-use)

-Bill (below is from Varta):

PS: I fixed a typo (I think) from Varta below--- 0/1 V should be 0.1 V

https://www.varta-automotive.com/bg-bg/Поддръжка/charging/how-to-charge-a-car-battery

Instructions on charging a battery safely

• Fully recharge the battery as soon as possible following each discharge
• Always check that battery charger is suitable for the battery
• Never use a battery charger without automatic shutoff
• An electronic voltage-controlled battery charger, preferably based on an IUoU charge profile, is recommended
• Charging to avoid acid stratification (not needed for AGM)
• Use a charger with IU characteristics and higher charging voltage (2.6 V/cell)
• This overcharge should only be used for a short time period to avoid water loss
• The open-circuit voltage after charge should be 2.12 - 2.13 V/cell
• For every 0.1 V difference to 12.7 / 12.8 V, the battery should be charged for 1 hour
• Never charge frozen batteries or batteries with a temperature above 45˚
• Connect the positive battery terminal (+) with the positive charger terminal, and the negative battery terminal with the negative charger terminal
• Do not turn on the charger until the battery has been fully connected
• When charging is complete, first turn off the charger
• Stop charging if the battery becomes hot or acid escapes!
• When charging, ensure good ventilation

Test a battery

The best and easiest way to test a battery is using a voltmeter or multimeter to measure the voltage. Once you know the exact voltage, use the table below to gauge the state of charge.

Make sure the battery is charged

To ensure that the battery can supply its stated starting power, it first needs to be fully charged. The recommended charging current is 10% of nominal capacity in amperes (e.g. a 4 Ah battery requires a 0.4A [Ampere] charging current). We recommend that you ensure your battery is fully charged before fitment to ensure a long service life.

• A new battery after activation is approximately 80% charged.
• Initial charging is always recommended. Never quick charge.
• You can find a detailed description of how to charge the battery in the instruction manual supplied with your battery.