Forum Discussion

wopachop's avatar
wopachop
Explorer
Apr 28, 2019

Whats normal voltage drop from a 4amp load? (210ah)

I have two brand new 6v from costco. I pulled 20amp hours out of them a week ago and then fully charged with an automotive battery tender.

Today i put a 3.8a load on them and voltage is down at 12.15v after a few minutes.

Are they supposed to sag that much under a little 4amp load? Did a quick search and all im seeing is topics about voltage sag while under solar power. My batteries are on the garage floor.

edit: I should have checked early. My watt meter is saying 12.15v.

But 2 multimeters are saying 12.27v and 12.3.
  • 2oldman's avatar
    2oldman
    Explorer II
    Apr 28, 2019
    wopachop wrote:
    It's a good safe way to charge the battery. Reputable company i feel safe plugging it in and walking away.
    You're going to have to tell us the amperage of the charger and how long you left it on. The week?

    wopachop wrote:
    Not a good way to maintain because isnt it around 0.5v too low for flooded?
    I don't understand this. You mean .5 amp?
  • wopachop's avatar
    wopachop
    Explorer
    Apr 28, 2019
    In a way you could argue the opposite regarding battery tenders and deep cycle batteries.

    Its a good safe way to charge the battery. Reputable company i feel safe plugging it in and walking away.

    Not a good way to maintain because isnt it around 0.5v too low for flooded?
  • MrWizard's avatar
    MrWizard
    Moderator
    Apr 28, 2019
    i have a 200amphr AGM, This Morning i have warmed up several cups of coffee in the MW and heated my jimmy deans breakfast bowl in the MW, i am using this PC, battery status is 24 AmpHrs used, 88% SOC remaining, 6 amp draw , voltage 12.63v

    your voltage
    that is too much voltage drop

    batteries were NOT fully recharged

    tenders are designed to maintain a battery that is fully charged
    NOT to recharge a battery that has been used
    voltage from a tender is NOT high enough to fully charge "any battery"
  • BFL13's avatar
    BFL13
    Explorer II
    Apr 28, 2019
    You are right, that is too much of a drop for that small load. Indicates the batts are not fully charged like you think from using that charger. You must use an hydrometer to determine the actual state of charge.

    You might not have a charger that can do it right.

    Pretend your 6s are Trojans (be similar for this work) and follow Trojan's instructions here

    https://www.trojanbattery.com/pdf/TrojanBattery_UsersGuide.pdf

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