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I am trying to replace a lithium-ion battery for my Bose QuietComfort 35 headphones. I cannot find the datasheet for it. The battery is an AHB110520CPS (AHB110520) by Synergy. It is supposedly an "Advanced Hybrid Battery" which uses thinner materials than LiPo or something.

Its specs are 495mAh 3.7V, max 4.2V (I think).

I could not find a datasheet or anything about it on the net, including at archive.org. The battery model is probably about 2 years old and could be obsolete by now. The manufacturer's website has some AHBxxxxx.. battery models listed but not this one.

Other numbers found on it:

  • 1ICR11/53
  • SYNERGY MH10048-E7
  • (chinese writing)

The battery has 3 wires labeled T (temperature), B+, and B-, so I don't think it has anything sophisticated inside it.

I would just replace it with a drone battery of similar capacity and voltage but I'm concerned about the charging current used for the battery. Do I have to find a battery with the same or more max charging current? I suppose I can measure the existing battery's charging current but what I'm curious about is what specs I need for the replacement battery in terms of charging current. I've read that lithium charging circuits are constant current/constant voltage (which is it?). So if the internal resistance of the battery is lower than the spec would there be a problem or not?

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  • \$\begingroup\$ Did you manage to successfully replace the battery in your QC35? Can you please provide us with some updates? \$\endgroup\$
    – wintermute
    Oct 10, 2019 at 21:28

2 Answers 2

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CC/CV charging means that it begins by providing a constant current until the voltage hits a preset level, then switches to that constant voltage until the current trickles down to something marginal.

The internal resistance of the battery doesn't affect the charging routine, although the charging efficiency might change.

This target charge current is relative to the battery capacity ("C"). For standard Li-ion or Li-polymer batteries, chargers often target 0.5C charge current. In other words, if the battery is rated at 500 mA-h, the target current is 250 mA.

It is not unusual to charge at 1C (500mA), but this compromises the battery's capacity over time.

I don't know about Synergy's "Advanced Hybrid" technology, but the voltages match standard Li-Po batteries. I would choose a new battery of (at least) the same capacity.

Hopefully you can find one that fits! Obviously, if you have to reduce the capacity to reduce physical size you risk charging the new battery too fast.

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  • \$\begingroup\$ I do have a remaining concern. How do I know it's charging at 250mA? It charges fully in about 15 minutes. Or at least it did shortly before it died. Still I remember it charging rather quickly even before this. Doesn't this indicate a higher charge rate? One drone battery I'm looking at of same capacity says max charge rate of 15A. \$\endgroup\$
    – Shorin
    Nov 4, 2018 at 12:36
  • \$\begingroup\$ I just checked this answer electronics.stackexchange.com/questions/24160/… and calculated the charging current to be 2A. That puts my fears to rest about the new battery with that 15A spec. Oh that would be for the battery with lower capacity though... So 2A is probably not accurate but at most it's 2A. \$\endgroup\$
    – Shorin
    Nov 4, 2018 at 12:41
  • \$\begingroup\$ @Shorin, 4C is a heck of a charging rate. Even RC quadcopter batteries usually have no more than 3C. You might seriously consider having proper thermal protection. The "15A" specs (~30C) has nothing to do with charging, it is discharge rate, which has a loose relation with charging. \$\endgroup\$
    – Ale..chenski
    Nov 4, 2018 at 17:50
  • \$\begingroup\$ @Shorin, as Ale..chenski says, that is a really high charge current. I wonder if there is a misunderstanding or an incorrect calculation. Do you have the equipment to measure current? \$\endgroup\$
    – bitsmack
    Nov 4, 2018 at 21:28
  • \$\begingroup\$ I think the 2 A charging estimate is in error. The device did charge itself in 15 minutes likely because its battery was dying and had very low capacity. The OP neglects to reveal which particular headphone does he have, and what kind of charger comes with it. It is likely a vanilla 500 mA charger, on par with regular USB charging. I really don't understand why people hide important information... \$\endgroup\$
    – Ale..chenski
    Nov 4, 2018 at 22:36
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Replacing a LiPo battery with bigger capacity is okay, since the device's charger likely would not know this, and will charge the battery with old current, which would be below the "safe charging limit", typically 0.5C as bitsmack already explained. So it will do no harm, it will just take a bit longer to complete full charge.

One word of caution however. Drone batteries usually have two leads only. Your device does have the third "T" lead. Usually the device charger expects certain resistance from the embedded thermistor for normal functionality, usually 10k. If the expected resistance is not there, the charger won't charge assuming the battery is faulty. But you can fool your charger by attaching proper (ordinary) resistor to ground, and everything should be fine.

You probably need to find a battery of certain dimensions, to fit into your device. This answer would help you to use numerical conventions used to size pouch Li-Po cells.

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  • \$\begingroup\$ Good point. Nice related answer, too :) \$\endgroup\$
    – bitsmack
    Nov 3, 2018 at 0:42

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