A 4 cell isn't enough battery. Considering warm up time, delay on the mock grid idling, a warm up lap, then an 8 lap race and even the possibility of a red flag and potentially more idling.....no bueno.
Even at idle you'll consume battery power. You can test what the current draw of the Dyna S is once the bike is running.
I made my own 8 cell batteries from DeWalt 36V packs when people were selling off excess batteries and they were cheap. Nowadays there are no deals but individual A123 26650 cells can be purchased but are often Chinese knock offs.
An 8 cell with my current ignition gives me minimum 45 minutes straight run time. I can get two 20 minute practice sessions or two heat races at least then I switch batteries. Recharge times are short with Lithium. They run out of juice quickly too, just like the engine is running our of fuel. I won't continue to use a battery if it shows less than 11.8V.
Don't recharge immediately after use, let it rest for 1/2 hr before charging. I've read that these batteries will continue as new for 1000 charges, so I won't use it for only one session then recharge, but try to discharge to a similar point if possible before recharging. A volt meter is your friend, as much as a fuel measuring stick, marked off in graduations.
I have always used a Battery Tender Plus, actually have two. Most big battery outfits recommend their special Lithium chargers, but I never bothered. It's been 6 years and they are still great. I did have a new small lead acid spare I used for practice that lasted only two years!
I am waiting for a response about another 8 cell battery and can let you know how that works out.
Here's a letter I received back from a Shorai rep about their batteries. Some honesty frankly. On the other hand the Batterystuff rep was "best of luck in your search"!! I didn't approach anyone else, but be forewarned before buying a battery to tell them it's for a total loss race bike.
Brent,
At this time, the LFX is designed for use as a powersports starter battery only and is not suitable for total loss systems. I do realize that some racers do us this (micro sprtint, vintage, and kart). They have the Shorai charger and a Sentry to make sure the battery is balanced and charged after each race.
Please see the below regarding actual capacity, howerver, to determine if this suits your needs.
Lithium Iron Phosphate has 1/3 the actual capacity of the lead acid equivalent and should not be used as a power supply in a total loss system (i.e. powering for lights, stereos, computers, etc.) Our LFX14 is 4Ah, the LFX36 is not 36Ah; it is 12Ah total and only 80% of that should be used before charging again. Our batteries should not be discharged below 12.86V or it will damage the cells over time.
It may be best to find a Lithium (energy cell) that has a lower discharge rate (anywhere from 2C to 10C is more suitable for your application) but has more capacity. Our batteries have a very high C rate (45C) for energy delivery to crank vehicles but low capacity for total loss systems hence they are not compartible for such usage.
What is the amperage draw as you may be able to use a 10C discharge rate battery. You may want to look into “CTC Batteries” (Try BatteryStuff.com) which are true deep cycle lithium batteries; they also have a low voltage cut off, and are lower C rate. You can’t start a vehicle on it but it will run as a power supply.
