Originally Posted by beedub
2015 Newmar Dutchstar 4018 with the battery bank for running most things off the inverter.
we only have power for a couple of hours and then black out.
Started the generator, charged them back up and again they only last for a couple of hours.
the panel for the batteries showed the charge level only came up to 6 out of eight bars at best.
Good advice has been posted above. There are lots of possibilities and so different conclusions.
Your last observation is the most telling. 6/8 bars may say,
Batteries are defective and not able to accept a full charge or charger is not working fast enough or able to provide a charge.
However, the conclusion depends on what you mean by "only came up to 6" bars. If your ran the generator for 2 hours and got only 6, that is to be expected for fully discharged batteries. If you mean you ran the generator for 8 hours and got only 6 bars, that could indicate something is not working properly.
To make it more complicated, there are three main battery voltage profiles. Your 8 bar gauge does not know the difference so the number of bars means something different depending on what is happening.
I will assume your batteries and charger are working fine for the following explanation.
Running the generator for 1 or 2 hour to "charge them back up" will partially charge the batteries. It takes more than 4 hour for an 80% charge. 4 hours may bring the bars up to 8 even though the batteries are not fully charged. When charging stops, "Surface Charge" will bleed off over the next few hours looking like batteries are discharging fast even with little or no actual usage.
If you can't get the bars over 6 while generator charging, it means the state of charge (SOC) is very low. It does not mean you have 75% SOC. Recheck the number of bars after an hour or more without charging. Bars will drop fast due to surface charge depletion.
The voltage profiles are:
Charging - charger is working
Discharging - charger is not on and significant loading is in progress
Static - neither charging nor discharging
Static voltage is when charging has been stopped for 4 hours or more and no significant discharge is happening.
SOC / Volts / Bars
0%/ 11.4 / 0 Batteries are discharged
50%/ 12.2 / 4 Batteries are at half charge level
100%/ 13.0 / 8 fully charged
Discharging voltage profile varies a lot. Discharging voltage will be below Static voltage. The higher the discharge rate, the lower the voltage will be. Inverter can draw large currents from the battery depending on what is running on the inverter. Battery at 50% SOC can be 11.4 volts when inverter is drawing high current. Inverter may trip to "off" when voltage reaches 11.4 volts. All 120 volt appliances will stop working. 12 volt lights will continue to work.
Charging profile applies when the charger is working to charge the batteries. This could be plugged into shore power, generator power, solar charging, or engine charging. You have mentioned generator charging and engine charging.
First, it takes 14 to 18 hours to fully charge lead acid batteries and lead acid batteries must be stored fully charged for long life. If you have stored your RV at less than the 14 hour full charge, then your batteries may be on their last legs even if they are not old time wise.
Charging profile is consistent, but depends on your equipment. Assuming you have a 300 amp hour battery bank and a 60 amp charger, your profile may be as follows.
0% SOC - Gen Charge - voltage starts at 11.4 volts / 0 bars
25% SOC - Gen Charge - voltage slowly rises to 11.8 volts / 2 bars / 1 hour
50% SOC - Gen Charge - voltage slowly rises to 12.4 volts / 5 bars / 2 hours
75% SOC - Gen Charge - voltage slowly rises to 12.7 volts / 8 bars / 4 hours
100% SOC - Gen Charge - voltage rises to 13.6 volts / 8 bars / 18 hours
Voltage will hold at 13.6 volts until generator is turned off.
Some chargers will reach 14.4 volts during the first 4 hours. They will then drop back to 13.6 volts for the remainder of charging.
Your charger and battery bank should show a similar charge profile.
Battery University https://batteryuniversity.com/
How does the Lead Acid Battery Work? https://batteryuniversity.com/learn/...ased_batteries
Charging lead acid batteries https://batteryuniversity.com/learn/...d_acid_battery
How to Charge and When to Charge? https://batteryuniversity.com/learn/...o_charge_table
How to Store Batteries https://batteryuniversity.com/learn/...tore_batteries
Summary of Do’s and Don’ts https://batteryuniversity.com/learn/..._battery_table