It's true that smaller cells provide less current than larger cells. When adding a second button cell, you're increasing the voltage and therefore increasing the ability of the battery's current to overcome resistance and reach the PCB/motor. As you add more cells, you reach a point where virtually all of the current that the tiny cells are able to provide is being used; at that point, adding voltage doesn't have any effect, and you only increase weight (though runtime may be slightly better). Three button cells is about the best performance you can get with this mod. It's also the easiest one to install.
Yes, using a more efficient motor really helps runtime. I use a motor from a cannonball clone, roughly a 2.2-2.6 I believe, and it has nice torque and good power usage. If you are only getting a 45-sec runtime, then you are not fully charging the cells. I regularly get 5-8 minutes of runtime before it starts to slow down, using a ac-dc charger and the formula found earlier in this thread to compute charge time needed. The voltage does drop off quickly as the cells lose charge, but if you charge them fully you'll get a lot more runtime before that happens.
That being said, the runtime will never compare to a fully charged 150mah battery, and you shouldn't expect it to. It is meant to be an easy replacement for the stock battery (50mah), with comparable runtimes. (You may have forgotten, but a stock car using a stock charger runs only a few minutes at a time.) If you want better runtimes for an endurance track, you can always swap out the button cells with a regular batt easily, since there is no soldering required. And a tri-button-cell car will *always* beat out a single cell car in a drag or short track by a wide margin.. just make sure you are getting it charged completely. Slower chargerate= safer, with best "topping off" ability. Faster charger= more likely to blow a battery, less likely to be able to top off the charge without going over or under.
You just have to keep in mind what this mod is for. Don't expect miracles, and you won't be disappointed.
