If a battery is charged, is leaving it in the unpowered charger going to cause any parasitic drainage? What happens when the charger is powered?
Yes it will.
If the charger is plugged in, the battery will remain charged indefinitely. Not a good practice though.
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Depending on the model, I guess. If you give me a couple weeks, I’ll test with two similar AA NiMH.
Purpose: To test if two specific chargers will eexhibit parasitic drain on, or discharge mounted cells while in an unpowered state.
Materials:
Opus BT3100
Xtar VC4
Cheap Harbor freight DMM
2Ă— Olight NiMH 2500mAh AA cells.
Methodology proposed:
To fully charge two pairs of respectively cherry picked AA NiMH of similar capacity and resting voltage. The CONTROL NiMH will be placed on a desk, the test NiMH will be left in the charging bay of an unpowered charger. Resting voltage will be tested each day for two weeks.
Results: TBD
Day 1:
Opus:
Control: 1.46V
Test: 1.46V.
Xtar:
Control: 1.46V
Test: 146V.
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Thanks for doing this. I’ve used a Battery Tender in 12V wet cells and wondered what would happen with dry cells.
Most chargers (any somewhat decent one at least) shut down once the charging current goes below a defined threshold in CV phase.
Whether or not they decouple the output from the rest at that point depends on the charger.
Rule of thumb: if the charger can still measure the battery voltage after charge completion, it will have parasitic drain (at least for the voltage divider to measure the output voltage). If it can’t keep reading the battery voltage after charge termination, chances are it is fully cutting off the cell and there is no drain.
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How would you know if the charger can read the voltage of the battery if its not plugged in?
If the charger is decoupled from the battery, does that also mean the battery is decoupled from the charger?
Is being electrically decoupled equivalent to being physically decoupled?
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Don’t leave the cell in the unpowered charger.
I’ve had high end survey equipment bleed a battery dry when left for a long time (months?).
I assume all chargers will drain the cell to some extent, until I see proof otherwise.
HKJ tested the unpowered current in all(?) reviews. Here’s one review as an example, bullet points 3 and 4 under “Measurements” list the drain for li-ion and NiMh cells.
https://lygte-info.dk/review/Review%20Charger%20LiitoKala%20Lii-500S%20UK.html
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Does that translate to built-in chargers - they are always connected to the battery, aren’t they?
Built in chargers are usually small integrated chip designs that are made to stay connected.
External chargers are mostly some microcontroller controlled devices that are rarely made to stay connected. A well made design could have a MOSFET that fully cuts the battery once unpowered, but I’m really not sure if any does (and which).
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That is a good question, it would be relatively straightforward to measure. I’m on a work site right now but might try to measure the current draw of my lights with built-in charging when I’m home in some weeks time.
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True, putting a (precise, uA capable) DMM between battery and charger is the easiest way to find out.
I think decoupling is mutual.