Artisan Power Polycom/SpectraLink 8400 Phones: Replacement Battery. Extended Capacity 2350 mAh Polycom/SpectraLink 8400, 8440, 8450, and 8452 Extended Capacity Replacement Battery Fully replaces battery number 1520-37215-001 and RS658. Lithium Ion Rechargeable Battery Pack | 3.6 Volt | 2350 mAh | Cells Made in Japan Longer Lasting: 2350 mAh capacity rating 31% higher than the OEM extended batteries, and 104% higher than the standard batteries. Manufactured by Artisan Power, a leader in premium quality replacement battery packs.