In Europe people need to go to tech inspection to check the voltage of their batteries before putting the car on the track. If the voltage is 0.01v over the limit it means not driving. In the past we have seen many drivers giving throttle in the walk to the control to lower the voltage a bit but with many competitions that is not alowed anymore.

the club in my area will sometimes check voltage too.. rules are clearly stated with a max voltage of 8.4V for the 1/10 track, my charger almost always cuts off at 8.41V ( I can't change the setting) and when they are teching the cars I just need to hit WOT a few times and that does the trick. Personally I think that 8.44V should be allowed because the rule says, 8.4V limit not 8.40V limit... <shrug>

Then it should be 8.49, not 8.44

my logic goes back to the days when I helped my son build pinewood derby cars in the cub scouts... they had a rule of 5oz as the weight limit and there was a speed secret of getting a scale that would read to 5.04oz and that would be legal because the weight would not round up... same logic would be applied to voltage if you don't specify the rounding to the nearest hundredth... 8.44V would round down to 8.4V when the precision is listed in tenths

HAHA, I gotcha, you are thinking the charger uses actual math rules and rounds up at 5 and doesn't just chop the last digit. I wonder....

If you crash more than once a race, the advantage of a battery charged to 8.8v is negated. I semi-regularly complete races without needing to be turn marshaled, and I have run 8.4v and 8.8v back to back and on a 14 second average lap track, the 8.8v packs are about .5 second faster per lap. Getting held up in traffic probably costs me the most time during a race day. My packs are usually still at 8.2v resting after a race.

If you are .5 second faster per lap the 8.8v packs on a 14 second average lap track, that adds up to quite a bit in a 5 minute race. Call it 4 laps per minute (estimated). That means you are going 10 seconds faster per race with those batteries. Almost an entire lap. I agree that not crashing, etc. is the most important thing to strive for. Going .5 second a lap difference just by charging batteries differently makes it worth charging the batteries at the higher rate. As long as your club allows it of course.

so whats the consensus on this now? Are more people using it now a days in races? Or just stick with the regular ol lipos? (14.8V 4s in my case)

Does anyone know a formula for calculating the difference in capacity (mah) when charged as LiPO (4.2v/cell) vs LiHV(4.35/cell)?

I don't believe there is a linear formula for this, you probably need to perform your own tests by fully discharging the pack and measuring the capacity that is placed into the same pack for each respective voltage.

There is a chart here which shows the point of diminishing return at about 90+ charge cycles where the capacity is about the same when charging at 4.35V as the cells tend to degrade faster as opposed to charging at 4.2V:
https://batteryuniversity.com/learn/...ased_batteries

Thanks, thats interesting. As SMC site hints, its clearly a marketing thing to be able to put a higher capacity on a battery. Generally, I'm in favor of smaller batteries/higher capacity if it means shorter lifespans.