Battery always sitting at half

mrk79ukmrk79uk Registered Users Posts: 2
Hey all,

Total newbie here but enjoying the learning. 

I've just fitted 3x 100w panels wired in series to my camper van along with a Epever tracer 40a MPPT controller and MT50. 

I have two sealed batteries in the back with a pretty standard split charge relay. 

I am finding that even after a long drive my batteries seem to read half full on the MT50. Does that indicate I have a faulty battery do you think? 


  • wellbuiltwellbuilt Solar Expert Posts: 581 ✭✭✭✭
    No the my 50 just Dosent read Accurately
     Check with a volt meter and I’m sure you will get a Accurate reading
    Out back  flex power one  with out back 3648 inverter fm80 charge controler  flex net  mate 16 gc215 battery’s 4425 Watts solar .
  • BB.BB. Super Moderators, Administrators Posts: 31,464 admin
    Assuming your sealed batteries are AGM (lead acid Absorbed Glass Matt) type... Then you should see around 14.4 volts (at 70F) for 2+ hours on the batteries to be fully charged.

    You can also monitor the charging current to the battery using a DC amp meter of some sort--And watch for 14.4 volts and the charging current to drop below ~1% rate of charge (i.e., 100 AH battery * 1% rate of charge = 1 amp).

    With Lead Acid batteries... You have 3 charging states:
    1. Bulk--This is below the charging set point (typically from ~12.0 to 14.3 volts) where the charging source outputs as much current as it is rated for to the battery bank.
    2. Absorb--This is where the charge controller "holds" the voltage setpoint for a number of hours (typically shorter time for batteries that are already full; and longer times for batteries that have been deeply cycled)l
    3. Float--This is around 13.6 volts or so and is to keep the battery charged (and the charging source will supply current to the DC loads when they are turned on--And continue to hold 13.6 volts, unless the loads are greater than the charging current).
    You can also measure the "resting voltage" of the battery bank. Let the batteries "rest" (no charging/discharging current) for 3+ hours. That voltage will be roughly the state state of charge. The voltage does depend on the type of battery you have (lead acid, sealed, AGM, GEL, Lithium Ion, etc.).


    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mrk79ukmrk79uk Registered Users Posts: 2
    Thanks, if it stops raining today I'll get the meter out and compare the reading with the MT50. 

    They are indeed AGM. 
    I will let you know what the outcome is.

    Thanks for the advice it's much appreciated. 

  • mcgivormcgivor Solar Expert Posts: 3,736 ✭✭✭✭✭✭
    The state of charge display is voltage based, being a reference only during charging not an indication at any other time, it may display 100% when in full sun but as soon as the PV input diminishes below what is needed to maintain the fully (apparent) charged state, it will begin to indicate a lower value even without loads.

    This phenomenon would also apply to alternator charging source, as soon as the engine has stopped charging the display will drop in as the voltage of the battery stabilizes to its resting voltage, which will be represented by a lower apparent value on the MT 50. To get any valuable information from said meter it must only be done during charging, everything other than that is null and void.

    Using a digital volt meter during charging will confirm that the battery is actually reaching it's required ~14.2V, or as specified by the manufacturer, as well as being held at that value for some time before transition to float, would be prudent . Always remember that the prime cause of lead acid  battery failure is undercharging, though with AGM overcharging is also a factor worth keeping in mind, however this is largely related to voltage, with a healthy battery it should self regulate current if voltage settings are correct. 

    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
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