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I need a replacement battery for an older laptop that originally came with an 11.25V Li-ion battery (presumably 3 cells at 3.75V each).

The batteries I found online mostly have a nominal voltage of 11.1V or 10.8V (i.e. 3.7V or 3.6V per cell). I did some reading and this could be due to a different chemistry (e.g. cobalt vs. manganese) or marketing strategies that favor higher watt-hours.

Many battery vendors list these batteries as suitable replacements for my model, but I'm concerned about the safety and potential risks of using a battery with a lower voltage:

  • Can these different voltage batteries (11.25V vs. 11.1V vs. 10.8V) be treated as equivalent/compatible for all practical purposes or will interchanging them cause a fire/explosion?
  • More generally, what kind of discrepancies in voltage are considered acceptable? Are there authoritative sources or recognized guidelines I could use to determine compatibility?
Giacomo1968
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Dejan Govc
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2 Answers2

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First, the ratio between 11.25 V and 11.1 V is only 1.3% ,and between 11.25 V and 10.8 V, 4%. The first is insignificant, well within tolerance of most electronic parts. The second implies a small drop in watt-hour capacity.

Second, modern chargers detect the rate of charge (as well as the voltage and current), and stop charging after the voltage has not changed for a period of time, protecting batteries, not only of differing chemistries, but of differing age, since the charge/voltage curve changes significantly with age. This means a modern charger is unlikely to overcharge a slightly lower voltage battery.

All electrochemical cells have a discharge curve, i.e. the voltage drops with state of discharge. A cell that reads 4 VDC (12 V in a three-cell pack) at full charge would read ~3.6 V (10.8 V for three) at 50% charge. A brand-new OEM battery, fully charged, would read ~12 V at full charge and ~11.25 V at ~80% charge (batteries are usually shipped partially charged, and it is often recommended that they be kept at 80% to extend the service life of the pack).

The batteries you've seen are unlikely to cause harm because of the voltage ratings, and might be rated at a different charge point, rather than having differing chemistries. That said, buy them from a reputable source, since a defective battery can certainly cause damage, or even fire!

DrMoishe Pippik
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These are most likely the same type or very similar. The voltage of a lithium-ion or lithium-polymer cell varies from about 4.2V when fully charged, down to 3.2V when fully discharged. There isn't "a" battery voltage, so we pick a place in the middle and call that "the" (nominal) voltage. Halfway between 3.2V and 4.2V is 3.7V. "Nominal voltage" literally means "the voltage written on the label."

If they chose a slightly different way to choose the voltage to write on the label, that doesn't mean the battery is different, just the label. However, it could be different. Li-Ion batteries are usually labeled as 3.7V nominal, and there could be a reason the manufacturer chose to write 3.75V instead. Halfway between 3.2V and 4.3V is 3.75V. Some manufacturers specify that you can charge up to 4.3V - whether the batteries are actually different, or whether it's just a marketing trick to write a higher capacity and shorter lifespan on the label, seems to be a matter of debate.

Ultimately, I'd trust the vendor's advice - if they seem trustworthy. If they're selling batteries that explode, they'd be in big trouble, even on a place like EBay. If many different vendors are giving the same advice, that makes it seem even more trustworthy.

Stack Exchange Broke The Law
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