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How to determine the health state of a LiPo battery?

obones

Hello,

I have taken out those two batteries from a device that needs both.
Clearly, the one on the right is dead and needs replacing.

image

However, I'm wondering about the state of the one on the left as it was manufactured at the same time.

Considering how expensive it is to come by the same model in France, I'd rather avoid buying two when one would be enough.

Here, I have a bench power supply, a bench DMM, an oscilloscope, a few ESP32s or arduino, even a RedPitaya but I doubt this one would be of any help here without specialized apparatus.

Many thanks for any suggestion.

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  • 0

    A full charge and discharge cycle  is the only way to know for sure how good a LiPo is.

    A visual inspection first will save you time and danger, get rid of the bloated one !

    To do the measuring properly you need a charger or a PSU that knows how to work like a charger and an electronic load which records the voltage during discharge and cuts off at the right cell voltage.

    For a good characterisation you need to be able to measure battery low frequency impedance during charge and discharge.

    A nice box that does it all will cost you £5k ish from Keysight, Keithly or R&S (NGM202 is nice).

    About the cheapest way is to use a programmable bench PSU for the charging and monitoring, there are some quite cheap electronic loads  - the cheapest from Farnell is £235.

    You could make a load yourself.

    Then you will need some software  - but you can get Claude (or other AI) to write that in Python quite easily.

    But by now you will be thinking that even in France buying 2 new batteries might be easier !

    What will be charging the battery when you use it ?

    MK

  • 0 in reply to michaelkellett

    Those batteries are from my neighbor's Visolux Digital xl fhd which includes its own charging circuit. 
    I tried starting it without any batteries while plugged to its AC adapter, but it stops right after the boot screen so I believe it needs to properly functioning batteries installed to work (hence the third wire, I believe).

    I had that 4 quadrant bench tool in mind as I read about it in a previous roadtest, but yes, it clearly is way too pricey for me.

    The seller's support was asked about and came back with a 230€ quote that I feel is completely off the mark, even edging on the side of elderly abuse. I mean, they already managed to get them to buy a new AC adapter for 104€ after three weeks of "inspection", which of course did not solve the situation.

    So here I am, trying my best to keep costs at a reasonable level.

  • 0 in reply to obones

    You can buy a similar rated LiPo battery from Amazon for about £10. It won't have the third (white) wire. According to Google AI the third wire will be for a thermistor. You can check this on the two batteries you have  - I assume that the thermistor will use the black wire as common but you should check (no volts between black and white, same volts between red and white and red and black with a high impedance meter.).

    Then get a suitable thermistor  - you might find some info as to what is typical on the web but you certainly don't want to characterise it by heating up a battery !

    If the device uses two batteries you should replace both of them so that the new ones at least have a chance of matching.

    Kudos to you for trying to sort this out - I hate suppliers who try and rip you off for spare parts.

    MK

Reply
  • 0 in reply to obones

    You can buy a similar rated LiPo battery from Amazon for about £10. It won't have the third (white) wire. According to Google AI the third wire will be for a thermistor. You can check this on the two batteries you have  - I assume that the thermistor will use the black wire as common but you should check (no volts between black and white, same volts between red and white and red and black with a high impedance meter.).

    Then get a suitable thermistor  - you might find some info as to what is typical on the web but you certainly don't want to characterise it by heating up a battery !

    If the device uses two batteries you should replace both of them so that the new ones at least have a chance of matching.

    Kudos to you for trying to sort this out - I hate suppliers who try and rip you off for spare parts.

    MK

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