FAQ
TL;DR: Tests show only 0.088 Ah—11 % of the advertised 800 mAh—under a 200 mA load [Elektroda, CMS, post #17262020]; “Most handheld multimeters draw just a few milliamps” [Elektroda, odalladoalla, post #17263475] Why it matters: choosing the wrong 9 V Li-Ion pack can give 10× less runtime than claimed.
Quick Facts
- Declared capacity: 800 mAh @ 4.2 V [Elektroda, CMS, post #17262020]
- Measured capacity: 88–449 mAh depending on 100–200 mA load [Elektroda, CMS, post #17262020]
- Peak charge voltage: 8.4 V (2 × Li-Ion cells in series) [Elektroda, krisRaba, post #17263233]
- Recommended discharge limit: 6 V (standard 6F22 spec) [OldSkull, #17262740]
- Typical price: ~26 PLN per cell (June 2018) [Elektroda, CMS, post #17262020]
Is there a boost converter inside the OKcell 9 V USB battery?
No. The pack uses two Li-Ion cells in series; output tops at 8.4 V and falls as the cells discharge. The only converter is a USB step-down charger on the micro-USB port [Elektroda, krisRaba, post #17263233]
Why does the battery show 8.4 V when fully charged, not 9 V?
Each Li-Ion cell charges to 4.2 V. Two cells give 2 × 4.2 V = 8.4 V. Marketing rounds this to “9 V,” but real voltage is lower [Elektroda, CMS, post #17263249]
What usable capacity can I expect at 100 mA load?
When discharged to 5.8 V with a 100–120 mA load, users measured about 449 mAh—56 % of the claim—before protection cut-off [Elektroda, CMS, post #17262020]
Why did I get only 88 mAh in my test?
A 200 mA load exceeds the pack’s 100 mA continuous rating, causing early voltage sag and capacity loss. Lower the current to ≤100 mA for realistic results [Elektroda, Kajox, post #17263849]
What is the maximum safe discharge current?
Sellers list 100 mA continuous; protection or voltage collapse occurs above that point [Elektroda, Kajox, post #17263849]
How often do I need to recharge the pack in a handheld multimeter?
Users report 2–3-month intervals with light meter use (a few mA draw), roughly matching 400–500 mAh effective capacity [Elektroda, dudik56, post #17262319]
Does the four-LED indicator show true state-of-charge?
No. At 7.8 V the indicator still reads 75 % even though many devices already warn of low battery [Elektroda, CMS, post #17262020]
What edge-case failures have been seen?
At least one cell dropped from 9.4 V to 0 V within seconds after charging—likely an internal short; a refund was required [Elektroda, dprzyb, post #17756342]
Will converter noise affect precision instruments?
Because this version has no boost converter on the output, there is minimal switching noise, making it suitable for multimeters [Elektroda, Ficu, post #17262565]
How do I dispute a faulty battery on AliExpress?
- Open a “Refund Only” dispute before confirming receipt and at least six days before buyer protection ends [Elektroda, CMS, post #17756675] 2. Upload photos or a short video showing voltage drop. 3. Request full refund; shipping back usually isn’t required.
Why does the pack self-discharge to 8 V within weeks?
Internal BMS and indicator circuitry draw micro-amps continuously; over several weeks this parasitic load lowers open-circuit voltage by ~0.4 V [Elektroda, CMS, post #17301906]
Is a super-capacitor 9 V replacement a better choice?
Super-caps offer near-infinite cycle life but provide milliamps for only seconds. For portable meters, Li-Ion packs still give hours of runtime [“Supercap 9 V battery”, Hackaday].
