The AAAA is a slim 1.5 volt alkaline cylinder, 8.3 mm across and 42.5 mm long, holding 500 to 600 mAh. Officially the LR8D425 or LR61, it is best known as the Microsoft Surface Pen battery and turns up in styluses and pen-style pointers.
AAAA (LR8D425), side view, drawn to scale: 8.3 mm across, 42.5 mm tall.
Voltage
1.5 V
Size (D×H)
8.3 × 42.5 mm
Chemistry
Alkaline (Zn/MnO2)
Capacity
500-600 mAh
Same battery, other names
Every code below is the exact same cell as AAAA (LR8D425). Any of them will fit and work identically.
LR8D425LR61MN2500MX2500E96Quadruple-A25A
Buying and replacement notes
Fun fact with practical value: standard 9 volt alkaline batteries from some manufacturers contain six AAAA-size cells inside, and hobbyists harvest them. The cells inside lack proper button tops though, so buy real AAAAs (Energizer E96, Duracell MN2500) for devices that matter. Slim styluses are sensitive to weak cells; erratic pen behavior usually means the battery, not the pen, is failing.
Commonly used in
Surface Pen and other styluseslaser pointers (pen style)glucose metersheadlamp gadgetshearing aid remotes
⚠️ Keep away from children. Swallowed button batteries, especially 20 mm lithium coins, cause severe injury within hours. If a child swallows one, call the 24/7 National Battery Ingestion Hotline (US) at 800-498-8666 or poison control at 800-222-1222 immediately. What every parent should know.
Frequently asked questions
What is the AAAA battery called officially?
IEC calls the alkaline version LR8D425, sometimes shortened to LR61, and ANSI calls it 25A. Retailers use E96 (Energizer) and MN2500 (Duracell). All are the same 1.5 V cell at 8.3 x 42.5 mm, one size slimmer and shorter than a AAA.
My Surface Pen stopped working. Is it the AAAA battery?
Almost always. A Surface Pen draws so little power that its AAAA lasts about a year, then fails with symptoms that mimic software problems: dropped strokes, no hover, intermittent buttons. Swap the cell before troubleshooting drivers; note the pen's polarity marking when inserting.
Can I use a AAA instead of a AAAA?
No. The AAA is 2.2 mm fatter and 2 mm longer, and it will not enter the battery tube of a stylus or slim pointer. There is no adapter direction that works either. Only the true AAAA size fits devices designed for it.