Need Help for Eneloop Battery Charging

fan8956 on 12/12/2021 - 10:51
Last edited 12/12/2021 - 13:42 by 1 other user

Hi all, thanks for your help in advance.

When my eneloop or ikea batteries just finish charging, if I take them our immediately and put them back in, all my smart chargers will then show they are just nearly full and will start charging again to top them up. You can do this multiple times… And this is especially true if I have left them in the charger for a while (this is more understandable to me as they might have slowly discharged). I highly suspect if you try it with your charges and batteries, they will do the same.

• So what is going on?
• Do we need to put them back in again and again manually to fully charge them or will I actually overcharge them?

• 

  Muzeeb on 12/12/2021 - 11:02

  Is it a smart charger or just a basic charger?

  • 

    fan8956 on 12/12/2021 - 12:05

    smart ones

    • 

      FLICKIT on 12/12/2021 - 22:34

      What make and model?

• 

  apsilon on 12/12/2021 - 11:22

  +3

  That's normal. An AA is a 1.5v battery but immediately after charging you'll likely find it's at 1.6 - 1.7v (this is how dewalt and others claim their 18v batteries are actually 20v) and it'll slowly drop back to it's normal voltage. By putting it back on to the charger (depending on the charger) you could shorten the life of the battery as you're constantly forcing it to a higher voltage.

  • 

    Catullus on 12/12/2021 - 17:19

    Excuse me, A dry battery, LeClance cell, Zn/C gives 1.5 volts and is not rechargeable. NiMH nominally 1.2v fully charged.

• 

  scrimshaw on 12/12/2021 - 11:29

  According to Wikipedia

  For NiMH batteries, the voltage of the battery increases slowly during the charging process, until the battery is fully charged. After that, the voltage decreases, which indicates to an intelligent charger that the battery is fully charged. Such chargers are often labeled as a ΔV, "delta-V," or sometimes "delta peak" charger, indicating that they monitor voltage change. This can cause even an intelligent charger not to sense that the batteries are already fully charged, and continue charging. Overcharging of the batteries may result. Many intelligent chargers employ a variety of cut-off systems to prevent overcharging.

  A typical smart charger fast-charges a battery up to about 85% of its maximum capacity in less than an hour, then switches to trickle charging, which takes several hours to top off the battery to its full capacity

  The handbook manual from Energizer details what kind of controls are used in their smart charger.

  Putting a fully charged battery into a charger may trick it into thinking the battery isn't full yet because the voltage monitoring data is missing from the previous charging session — your charger will instead look for a further voltage drop before it knows that the battery is already full.

  There's also some useful information on this site https://eneloop101.com/charge/

• 

  techno2000 on 12/12/2021 - 11:33

  +4

  Every charger behaves a bit differently with respect to detecting full batteries.

  I thought my old eneloops were losing charge sitting in the drawer because when i put them in many of my newer usb smart chargers they sat charging for nearly 30 min or more before they showed full.

  But when i dug out my old Maha C9000 charger and tested it immediately stopped charging and showed full after 5 min or so.

  So stop putting full batteries again and again in to your chargers.You are damaging them that way.

  Let go of your OCD.Now i just use my batteries from my drawer and when they need to be charged i just drop them in to any charger and then when its full just store them back in my drawer.

  Life is too short to worry about charging idiosyncrasies.

  • 

    jizmo on 12/12/2021 - 11:55

    -1

    OCD OCD? Really I thought it was UCD Under Charge Disorder! What are you going to do if your remote suddenly dies when the most annoying ad ever made in the world channel 10 "I'm a celebrity get me out of here " starts and can't change channels because your batteries are low.
    You'll be the one with the poisoned brain not Mr UCD.

• 

  ZDC on 12/12/2021 - 23:01

  Depends what kind of charge algorithm is used. -dV/dt is a fairly common termination algorithm to use for Ni-MH and it sounds like your smart charger uses that. If you look at a graph of voltage vs time when a Ni-MH cell is charging, the voltage of the cell will rise, begin to plateau, and then drop a little (by a few mV). The charger uses this drop in voltage to detect when the cell is fully charged, hence the name -dV/dt.

  When you plug your fully-charged cell back into the charger, it has to look for this drop in voltage again before declaring the cell fully charged. Depending on your charge current and -dV/dt sensitivity, it can take anywhere from a few to tens of minutes to detect a fully charged cell.

  EDIT: To answer your question, you are indeed over charging your batteries slighty by doing that. By nature, -dV/dt very slightly over charges the cell. Therefore, your cells are 100% charged the first time, even though it might not appear to be the case.

• 

  lgacb08 on 12/12/2021 - 23:03

  +1

  nimh battery are very difficult to determine when it's fully charged because the voltage curve is almost flat, the charger can only determine this after charging it for a period of time and based on the slightly drop in voltage when it reach 100 and stop charging. When you took them out, the charger had to put current into it again for a time to identify this drop and stop, but no matter how many time you put it in, the marginal gain in capacity is negligible, even when put them into charge when it's near full doesn't give it much extra juice.