diagnose my fazer fault

[Keir]

25 mile journey @ 75mph
10 miles or so in and the bike starts to loose power over about a mile.
power is down and i can fell it struggling on a smooth throttle.
I pull in and it dies.
wont start just keeps turning over
i wait 5 mins and it starts again but runs badly, sounds like its on 3.
i rev a couple of times and it clears and im on my way to complete the journey without a problem.

this has happened 4 times now. each time i wait then carry on, its getting annoying.

bikes standard but running on a DRZ battery which is marginally smaller. its been running fine on this for 3 months until this week. its fully charged. not sure if this affects things.

ideas?
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Current : '08 Yamaha FZ1s
Previous: '99 Honda CBR 600FX, 03 ZX636 B1H, 99 Fazer 600 (red), 02 GSX-R 600 K2, 00 SV650s (red), 2008 ZX10R, 97 Bandit 1200N, 04 ZX6RR K1H, 04 GSX-R 1000, 98 Fazer 600 (gold), 05 Madness 110 Pit bike, 04 CR125R, 00 SV650s (black), 06 KTM 625 SMC, 99 SRAD 600 track bike, 03 SV650, 98 Bandit 1200N, Bandit 600SY, 03 GSX-R 600 K3, 01 GSX-R 600, 01 Fazer 600 (black), VFR 400 NC30 x3, 78 Honda Dream, 00 Speedfight 50