When the lead acid battery was going bad on my BBT starter, I looked into purchasing one of the Alien Motion batteries (and charger) to save weight. While there is nothing wrong with the AM battery, it's quite expensive, then you have to buy their charger extra.
I found this LIth Ion battery pack at Harbor Freight for jump starting cars. It has a CCA rating of 400, where the lead batteries are usually around 180 CCA.
The lead acid battery weighs around 10 pounds. This LI battery only weighs a pound! So the total weight of the starter and battery is right around 10-11 pounds! Half the weight!
Obviously there is a little bit of wiring that needs to be modified by cutting off the automotive style ends and crimping on basic eyelet terminals, but it's pretty straight forward.
The only drawback, and to me it's very minor, is that you have to turn the jump pack "on" to use it every time. Where the Lead battery is "hot" all the time. The sequence is push the gold button close to the end for about 3 seconds, then push the red button in the center for about 2 seconds. LED lights will light up to let you know if you've held the buttons long enough. The jump pack will auto time off after about a minute or so.
This new battery turns my animal over without any problems at all. I figured if it can turn over a car engine with 8 cylinders, my kart motor would be a breeze!
It comes with a 110v wall adapter, so charging is easy. I charged mine towards the end of August and only ran a few weeks until our season ended here in PA mid September. For kicks and giggles, I turned the jump pack on today, and it still shows full power! There are 4 blue LEDs on the pack to show battery level.
The regular price at HF is around $80, but you can find them on sale for $60, so be patient!
The HF item number is 62749.
I just used a couple bigger zip ties to hold it to the starter. It only weighs a pound, so no need for overkill.
Hope this helps the seemingly endless saga of the short life lead battery.
Disclaimer: legal mumbo jumbo, if you think you can do this, you probably can. If you don't like playing with electricity, get a good buddy to do it for you. As always be careful and do this at your own risk.