I just want to sum up some infos on LiPos and the issues with the Summit.
Every motors needs power and it really don't care if from LiPo, NiMh or other sources. Then it needs a Electronic Speed Controller. You can get those for brushed motors and for brushless motors. Some ESC are programmed to cut off power if the voltage gets too low. The EVX-2 doens't have this option. The VXL (Summit 1:16) has this option, the ESC can be "reprogrammed" using a button to have low voltage cut off (for LiPos) or just let the battery run dead (NiMh).
One issue with the low voltage cutoff (LVC) or a low voltage alarm (LVA) is that LiPo cells are added serial to a pack like 2S1P. This means you have two cells in a pack. LiPo batteries have the tendency that the cells of a pack don't discharge evenly.
So you check your voltage on the LiPo and see 6.3V so you asume that each cell has 3.2V and you can drive some - then you check every cell and you see 3.5V and 2.9V - LiPos under 3V often can't be recharged, the whole battery is dead.
So a LVC should base on CELL info and not on battery info. To prevent some of these issues, LVC are often set "high" like 7V because it's very likely than both cell are close, so even 3V/4V is a lot less plausible than 3.2V/3.8V. So a 7V cutoff is pretty safe.
Back to our summit: We don't have built in LVC or LVA
How to handle this? Here's a history of my approaches.
1. drive till power-loss ($free)
I did this once or twice, a cell dropped to 2.8V and I was able to bring it back but I didn't feel that confident...
2. trust and pray and check ($voltage meter or $25 for hk-010)
I just drive around and after like 30' I pop the hood and connect the balancing tap to HK-010 Voltage Analyzer (basically a volt meter than doesn't connect to the battery tap but to the balancer tap). After some packs, you get a feeling and I always stop around 7V or when one cell drops below 3.5V.
3. lipo alarm #1 "7.4V-11.1 RC Lipo Battery low Alarm Indicator buzzer" ($3)
Bought a lipo alarm off ebay. I connected it but as soon as I pull the trigger hard and the truck jumps the gun, the alarm sounds. So the "electronics" of this cheap device can't handle the voltage drop when accelerating. Some $ wasted, I don't mind.
4. voltage display "Battery Voltage Indicator Checker Tester For 2S-6S Lipo" ($2)
I am very happy with these, they simply display cell voltage and battery voltage in rotation. I use two zip ties to build two "rings" so they don't fall off when one ring goes around the power cable. The display is pretty accurate, no alarm but using my method of attatchment you can even see your voltage from 10 feet away so after some bashing and crawling I simply turn the truck, look under the skirt and see how the batts are doing. I only connect to the BEC side.
5. NOVAK (#5470) 2-Cell LiPo Smart Stop ($25)
I didn't check this out yet, some guys say it's worth, some say that Novak doesn't recommend it, some say to go with 4-cell smart stop while other say to simply us the BEC side. I have one on my desk but didn't feel soldering it yet.
6. MTTEC Lipo-Wächter BS6 V4 ($40)
Bought in Europe, this lipo alarm is very "custmizeable": You can chose the voltage and the time the cell has to be below this voltage so you omit the problem with the cheap guards that immediately sound when the battery is under pressure.
My setup today:
BEC side: I run the MTTEC (#6) with 3.5V warning and 3.5s delay and 2s "beep"
Non-BEC side: visual control using voltage display (#4). I like those.