GBA CleanJuice. Designed and tested in the UK by a reputable modder and builder, the RetroSix CleanJuice for GBA is the ultimate upgrade to your console. Connect battery to CleanJuice board (only fits in one way so don't worry).
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3.7V 850mAh Rechargeable Li-ion Battery Pack For Nintendo GBA SP Gameboy Advance SP Replacement Batteries with Screwdriver
Aliexpress UK
Not compatible with Nintendo DS Lite and non-SP versions of the GBA. AC Chartger adapter-. Battery Type : Li-ion. 1X AC ADAPTER.
eBay
High-Performance For BOSCH 18V 6.0Ah LITHIUM-ION BATTERY GBA 18V 4.0/5.0 Ah Professional GBA GSR GSB BAT609 Rechargeable Battery
Aliexpress UK
BAT411, D-70745, BAT411A, BAT412, BAT412A, BAT413, BAT413A, BAT414. GDR12V-Li-ion, GDR10.8-LI, GDR 12V-Li-ion, GDR 10.8-LI, GDR 12V-Li. GSR12V-Li-ion-2, GSR12V-Li-ion, GSR10.8LI, GSR10.8-LI, GSR10.8-2-LI, GSR 12V-Li-ion-2, GSR 12V-Li-ion, GSR 10.8-LI, GSR 10.8-2-LI, GSR 12V-LiQ, GSR 12V-Li-2, GSR 12V-LI.
eBay
8pcs LiitoKala 3.2V 100Ah 105Ah lifepo4 battery cells DIY 12V 24V 48V electric vehicle RV solar cell pack EU/US duty-free
Aliexpress UK
BOSCH COOL PACK GBA 18V 6.3AH ENERACER BATTERY 1600A00R1A 3165140885720
eBay
Long-Lasting Backup Power: 6,500 mAh capacity, up to 6 months of use from a single charge. Easy to Install and Remove: Intuitive clasp is designed to be simple and quick to use. Charge with USB-C: Power it up with the same cable you use for other...
eufy
Third party/unofficial (as in not made by Nintendo) but fully compatible and has a higher capacity than the original battery (850mAh vs 600mAh).
eBay
1500mAh Rechargeable Lithium Battery For GAMEBOY ADVANCE GBA GBC GBP charging Module Support original shell
Aliexpress UK
Easy to pop on and off of your console. It is the battery cover only. Get in Touch.
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850mAh Rechargeable Lithium-ion Battery + Tool Pack Kit for Nintendo Gameboy Advance GBA SP
Aliexpress UK
Specifications: Voltage: 80V Capacity: 3000mAh Battery type: Li-ion Weight: 1350g per battery Replacement for: GreenWorks GBA80200/Pro 80 Greenworks G80B4 Greenworks GBA80200 Greenworks GBA80400 Greenworks GBA80500 Greenworks 2901307 Greenworks 2902407 STIGA SBT 2580AE SBT 4080 AE SBT 5080 AE Compatible with GreenWorks: 2901302 Akku-Heckenschere GD80HT Akku-Kettensäge GD80CS50 Akku-Laubbläser GD80BL GD80BP GD80BPB Akku-Rasenmäher GD80LM46SP GD80LM53 Rasenmäher 46cm SP 51cm SP GD80LM46SO GD80LM51SP GD80LM53 Akku-Rasentrimmer GD80BC GD80BCB Akku-Schneefräse GD80SB GD80ST STIGA Akku-Heckenschere SHT 80 AE Akku-Kettensäge SC 80 AE Akku-Laubbläser SAB 80 AE Akku-Motorsense SBC 80 D AE Akku-Rasenmäher Combi 43 AE Combi 43 S AE Combi 48 AE Combi 50 S AE Multiclip 47 S AE Multiclip 50 AE.
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AGS-003 Rechargeable Battery 850mAh 3.7V Lithium Battery For Nintendo GBASP Game Console Boy Advance GBA SP Built-in Batteries
Aliexpress UK
For GBA SP. Battery Type : Li-ion. 2 x Battery. Fit Model Warranty: Full One Year ( 12 Months ).
eBay
Battery Adapter for Bosch 18V GBA Li-ion Battery Converter to for Einhell 18V Lithium battery Power Tools Drill
Aliexpress UK