Micro USB rechargeable 9v battery £4.26 @ Unitek store / AliExpress
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Micro USB rechargeable 9v battery £4.26 @ Unitek store / AliExpress

10
Edited by:"WizardOfWelshness"Found 1st Dec
Or £7.41 for 2pcs. Actual capacity is between 400-500mah (about normal for a lithium battery of this size) but still a good price for that spec, convenient recharging using a standard micro USB cable... ideal for low drain/consumption devices EG. toys, smoke alarms, multimeters, Electric Guitar, RF microphones Ect.... there is a slightly more expensive option on Banggood with charging progress and capacity check LED's for just over a quid extra, and that link is here. banggood.com/OKc…tml


Edit. i've just checked that link again and it seems the seller has now decided to add a postage cost (was free shipping)... the Banggood link is still good (and free shipping) and has the benefit of the test LED's. WM.

Top comments

This won't be suitable for smoke alarms. They rely on a voltage dropoff to trigger the beep to remind you to change the battery. This will just be cut off by the circuitry when it hits the cut off voltage. This may leave you with a smoke alarm that you think is functioning but is not.
10 Comments

Great idea. I believe the charging voltage must be higher than than the battery voltage so there must be some sort of booster circuit in the battery to up the 5v to 9v+. This obviously cuts down on the size of the battery cell and hence its capacity. Unless the battery is slightly larger than a normal 9v battery.

Why is this not a thing

postage extra 3.5$

This won't be suitable for smoke alarms. They rely on a voltage dropoff to trigger the beep to remind you to change the battery. This will just be cut off by the circuitry when it hits the cut off voltage. This may leave you with a smoke alarm that you think is functioning but is not.

TiptreeJam3 h, 40 m ago

Great idea. I believe the charging voltage must be higher than than the …Great idea. I believe the charging voltage must be higher than than the battery voltage so there must be some sort of booster circuit in the battery to up the 5v to 9v+. This obviously cuts down on the size of the battery cell and hence its capacity. Unless the battery is slightly larger than a normal 9v battery.


They should not be a lot smaller as 9v batterys comprise of multiple lower voltage cells that the 5v charges with probably a few diodes for switching. I bought the ones from banggood as they do free shipping

Best to note the disclaimer: "Due to stock clearance, real capacity maybe 400-500mah..." not the 700mah claimed

TiptreeJam5 h, 59 m ago

Great idea. I believe the charging voltage must be higher than than the …Great idea. I believe the charging voltage must be higher than than the battery voltage so there must be some sort of booster circuit in the battery to up the 5v to 9v+. This obviously cuts down on the size of the battery cell and hence its capacity. Unless the battery is slightly larger than a normal 9v battery.


Cell charge voltage 4.1/4.2v easy to get from 5v . But 3 cell output would be 10.8 so must be regulation on output

Original Poster

TiptreeJam7 h, 6 m ago

Great idea. I believe the charging voltage must be higher than than the …Great idea. I believe the charging voltage must be higher than than the battery voltage so there must be some sort of booster circuit in the battery to up the 5v to 9v+. This obviously cuts down on the size of the battery cell and hence its capacity. Unless the battery is slightly larger than a normal 9v battery.


There's a 2S Lithium polymer cell internal to the casing, this limited space inside is reflected in the maximum capacity, you won't get much more than about half an amp (500mah) at that rated voltage (2s).
The 5v USB input is boosted as a 2S charger, high voltage cut-off for lithium is 4.2V per cell = 8.4v full charge, not checked the discharge cut-off voltage, so good point to you too GavinL, but it's much lower than a smoke alarm low battery warning... i've been using this type of cell for around 2 years in 3 different smoke alarms and the short "peep" every few mins reminds you to charge.... the battery still shows half in the bank however (i bought the LED version @ about £3.50 each on offer). only charged 2 of them once since installation.
Tried, tested and highly recommended... i bought another 2

drivel2 h, 57 m ago

Best to note the disclaimer: "Due to stock clearance, real capacity maybe …Best to note the disclaimer: "Due to stock clearance, real capacity maybe 400-500mah..." not the 700mah claimed


Typical 'clauses', huh?. :-(

Lol.

For the Banggood battery Code 2017cyber9% reduces the price by 9% (down to £4.84), if you haven't used it already, otherwise use AFFILIATE6 which knocks 32p off the price (down to £5). Quidco or TopCashBack (6%/6.06%) may give you up to 30p back if you go through them as well.
Edited by: "fablanta" 2nd Dec
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