In the event that you've had the "red ring of death" while on a gig (low battery) and had to change them on the fly--not fun. My first/last time was on a fairly dark stage, which didn't make it any easier. You can order an extra battery holder and keep it loaded for a very fast swap. The part # from Yamaha is WS668000. I think it's about $12. Well worth it IMO.