I've read War and Piece on such over the last twelve months and in the end there's only one way to find out turned up today even on our bathroom scales the original battery comes in a 3kilos and the lithium can barely move the needle but hopefully I'll get them weighed properly tomorrow and having loaned out my tester I'll check the voltage( it tells you too on the clues) as well before fitting,it looks like and interesting learning curve.

Interesting to see how it cycles, cranks and handles long loads from accessories etc, curious about the results myself.
Do you have a link or number for the exact battery?
Please keep us informed as to how it goes!
Matt.

As far as im aware lithion technolgy puts the same power out right till then end and then suddenly cuts off so you wouldnt get warnings like alow cranking it would just stop all power

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Yamaha xt660x 2009 blue/gold mods= iridium plug, stage1+2, removed snorkel, blocked ais, akrapovric pipes, power commander pc3usb (pre made map), adjusted tps, dynojet 02 optimiser 30amp aux relay, smoked puig screen, oxford heated grips and brembo carbon ceramic pads, rfx 30mm bar raisers, puig long adjustable leavers, plus much more and a cheep �30 alarm which stopped it been stolen

Hence why I'm trying one on my XT first to see how it goes,but having ridden down to Portsmouth a couple of years ago on a K1200r stopped for fuel at Sutton Scotney and then a top up at the Shell garage just around the corner from the docks the battery completely fell off a cliff absolutely stone dead so I can tell you gell batteries most certainly stop all power with no warning.

I had a Shoria lithium iron battery in my 990 SMR for 20 months & transferred the same battery to my 990 SMT for the past 10 months & not had one problem with the battery, I know guys have had problems in colder countries where the lithium iron batteries don't like the cold.

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Mods that I have done to my XTX's

My 04 XTX
Stage 1 & 2 DNA filters / Kev fuel mod / snorkel mod / Drilled air box mod / Engine breather mod / Fork Spacer mod / 15w fork oil /
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My 07 XTX
Raptor 700 cylinder 102mm / Modified Crank Case to take a 105mm Raptor Cylinder / 11:1 102mm JE Raptor piston / Stage 1 Raptor Hot Cam / Ported head / Colder Spark Plug / +2mm Throttle body / DNA stage 1 & 2 filters / Modified Air Box / Snorkel removed / Worry Brothers stage 2 filter cover / 6mm & 8mm Bolts Replaced with Titanium Bolts / Recovered seat in Black / O2 Eliminator /

My 09 XTX
59HP at the rear wheel / Stage 2 Raptor Hot Cam / DNA stage 3 Air Box / Carbon Can Exhausts / Modified Exhaust Link Pipes / PCIII With Custom Fuel Map / Wideband Commander O2 Data logger / LCD100 Dyno Jet display & fuel adjuster / 2500 OHM HT lead instead of a 10K OHM XT lead / Extra Coolant Cooler / Protaper Fat Bars / Tail Tidy With LED Tail Light / OKE Protection Knobs / LED indicators / AIS blocked / Modified rear sprocket rubbers / Rear Foot Pegs removed / 09 ECU With 02 Sensor Changed To A 06 ECU / Complete wiring harnes Changed from 09 to 04 / Home made LED resistor flasher / Hole drilled in the fuel tank filler neck to allow quicker filling / Modified Bar End Weights / Progressive front fork springs, 15W fork oil, forks lowered 25mm, used XTR rear links lowering the rear 20mm, rear spring one click stiffer / Changed front & rear guards from blue to black / 47T rear sprocket / Speedo Healer V4.0 / Kev throttle cam mod / Throttle grip mod / The new 2010 O2 sensor mod is out, works a treat, The new 2012 O2 Controller is out, PM me for details

Now ride a 2018 MT09SP ABS + TCS

My KTM 990 SMR Mod book. http://www.ktmsmt.com/viewtopic.php?f=13&t=4946

Stock battery came in at 3.4k the Lithium was 671grams

Just go into ebay and put lithium battery XT660 it'll show your options,I didn't get mine from there but it gives you an idea