How come my rechargeable battery self discharges so fast?

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Discussion Overview

The discussion centers around the rapid self-discharge of a rechargeable NiMH battery used in a piezoelectric energy harvesting project. Participants explore potential reasons for the observed voltage drop when the battery is removed from the charger, including charging practices, battery condition, and self-discharge rates.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant notes that their NiMH battery voltage drops significantly after removal from the charger, prompting questions about the cause.
  • Another participant references self-discharge rates for NiMH batteries, suggesting that the observed drop may align with known behavior.
  • Concerns are raised about the possibility of battery damage due to overheating during charging, which could affect performance.
  • Some participants argue that the voltage reading of 1.2V does not necessarily indicate a fully charged state, suggesting that the battery may not be adequately charged.
  • There are discussions about the efficiency of the charging process and the importance of measuring charge current to assess battery health.
  • A participant suggests that the self-discharge rate may be significant compared to the charge current, potentially leading to rapid voltage drops.
  • Another participant questions the assumption that 1.2V corresponds to 90% charge, advocating for charging until the voltage stabilizes.

Areas of Agreement / Disagreement

Participants express differing views on the charging state of the battery and the implications of self-discharge rates. There is no consensus on whether the battery is functioning correctly or if the observed behavior is typical for NiMH batteries.

Contextual Notes

Participants mention various factors that could influence battery performance, including temperature during charging, the method of charging, and the characteristics of the energy harvesting setup. Some assumptions about the battery's state of charge and self-discharge rates remain unresolved.

Who May Find This Useful

This discussion may be of interest to individuals working with rechargeable batteries, particularly in energy harvesting applications, as well as those exploring the characteristics and limitations of NiMH batteries.

  • #31
When brand new, the cell has been self-discharging on the shelf for as long as it has been since it was charged at the factory. And, they may not have charged it to 100%. 1.27 volts is just what it happened to be at when you measured it. It has no meaning.

You need to fully charge it with a NiMH charger if you want to characterize it.
 
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  • #32
NascentOxygen said:
You are placing too much reliance on that voltage. It's more of a guide for a typical cell. The best way to estimate a cell's state of charge is knowledge of the charge you have put into it, and it seems you are delivering minimal charge from your novel source.

meBigGuy said:
When brand new, the cell has been self-discharging on the shelf for as long as it has been since it was charged at the factory. And, they may not have charged it to 100%. 1.27 volts is just what it happened to be at when you measured it. It has no meaning.

You need to fully charge it with a NiMH charger if you want to characterize it.

Thank you all for sharing. i think i need to find other source to verify. Since the source that i found is unsustainable.
 

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