Renogy 200 ah AGM

papab Registered Users Posts: 66 ✭✭
Anybody have experience with this Renogy 200 Ah AGM?
Curiously they rate it at 200 ah at a 10 hour discharge rate instead the typical 20 hour.   They say it's 'specifically designed for solar energy storage applications',  but they don't go into details so I'll just take that as marketing BS.   Similar, but not exact stats as the UPG battery in the other thread,  a little heavier.


  • Marc Kurth
    Marc Kurth Solar Expert Posts: 1,143 ✭✭✭✭
    edited September 2019 #2
    Their data shows that if you discharge their battery by 30% (30% DOD), the storage capacity will drop to 80% after only 1,000 charge/discharge cycles. So, that is a little more than 2-1/2 years of daily discharges.
    Their graph also shows that if you cycle down to 50% DOD daily, their battery will be down to 80% storage capacity in 15 months.
    It is my opinion that the DOD/Cycle Life tests conducted per BCI standards are not realistic for offgrid systems. In general, cheaper AGM's will give you around 70% of the test values. Higher end AGM's will run closer to 85% of the test values. (I can explain why I feel this way if anyone cares) Note that their published data does not indicate what the test method was.
    I would think that these batteries are just another re-badge from Vision Battery in China, like so many others.
    I am looking forward to hearing from others with actual hands-on experience with these batteries. I just shared a whole lot of theory, BUT that is not what you asked for! So my reply probably should have been: "I have no idea!"  :):smile:
    I always have more questions than answers. That's the nature of life.
  • papab
    papab Registered Users Posts: 66 ✭✭
    Mark, I would like to know your reasoning.  I'm not surprised though, I would assume that the BCI test is a discharge followed pretty close by a charge which would be much less stressing than a slow overnight discharge followed by a relatively slow charge
  • Marc Kurth
    Marc Kurth Solar Expert Posts: 1,143 ✭✭✭✭
    Yes, that is a big part of it, but there is more. Using easy, round numbers for talking purposes:
    If I drain a given battery from 100% to 0% in 24 hours, I get 100 AH out of it.
    If I drain that same battery from 100% to 0% in 1-2 hours, I will get closer to 80 AH or 85 AH.
    Now, lets repeat that process 1000 times.
    The slow drain gave me 100 AH x 1000 = 100,000 AH
    The slow drain gave me 80 x 1000 = 80,000 AH
    That's a big difference in total AH pulled from the battery over a battery lifespan.

    Battery warranties are heading toward total watt hours provided. Some are already there - which totally makes sense.
    I always have more questions than answers. That's the nature of life.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    And you have to watch the math here... Watt*Hours vs Amp*Hours...

    More or less, Lead acid batteries are (to a first degree) Amp*Hours in = Amp*Hours out (they are charge flow efficient). Only when you charge > gassing voltage, then do the Lead Acid Batteries become less efficient (i.e., charging current in releases Hydrogen and Oxygen gases, that you never can "recover" and current flow).

    Now, when you look at energy---Power (Watts) = Voltage * Current and Energy = Voltage * Current * Time (typically, for our needs; Volts, Amps, and Hours).

    So when a battery starts at 100% SoC and Vbatt-full=~12.8 volts (lead acid 12 volt battery), and discharges to Vbatt-empty=~10.5 volts, the total energy (Watt*Hours) is dependent on battery voltage, current draw, internal resistance, chemistry activity, etc...

    For "the old fashion" usage of batteries--Filament lamps, electric motors, tube radios, etc... The Amp draw from the DC loads are (sort) fairly consistent. At 12.8volts, you get 10 amp draw, and at 10.5 volts, you get a 10 amp draw--The the "description of battery performance" in Amp*Hours is good enough for those loads.

    Today, we have a lot of constant power loads... LEDs, Computer, and the general catch all of AC Inverters.... For example, you want to run a 10 amp load at 120 VAC... That is 120 Watts. The inverter DC input current requirements are "variable". Ignoring efficiency and stuff for the moment:
    • Power = Volts * Current
    • Current = Volts / Current
    • 120 Watts / 12.8 volts = 9.375 Amps
    • 120 Watts / 10.5 volts = 11.43 Amps
    So, something that I have noticed over the years (may have been many decades ago--And I just did not pay attention), now battery systems that are for UPS systems (basically AC Charger->Battery bank->AC Inverter), where the AC inverter is modeled as a constant power source, I am seeing batteries defined in Watt*Hours per cell (or per battery)...

    A more "accurate" number for our "modern AC constant power loads".

    Since we are generally working with rules of thumbs here... Call a 12 volt battery "12.0 volts nominal" discharging and "14.5 volts charging" (for flooded cell)--Sort of gives us a "good enough" estimate of battery performance when doing the "solar math" without too many confusing (and over conservative) fudge factors thrown in.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset