I found this here site about on nicad batteries, which offers the following facts, nicads are supposed to be run down to no less then 1% of charge before recharging, the advice on the site i found was to run down the device until it started slowing down or almost stopped, but not left on until the battery is dead...Here is the site i found, about Nicads,
http://www.hardwaresecrets.com/article/ ... ries/292/2
Also it says Nicads have a life of no more then 500 charges and charging too often or too soon shortens their life. They lose 1% of charge per day or about 33% per month. (So i guess you'd want to charge them every two months or so-even if you are not using it-because once nicads are dead, there's no more recharging, they remain dead).
I have a VOM (volt ohmmeter or multimeter instrument)and know the basics but apparently its tough to reliably measure the state of charge on a nicad. Because they stay at a measured 1.2v per cell, all the time you are using the device it powers, right up until they drop to 1% (time to recharge). In other words, you could drive the tank for 5 minutes, then 10, then 20, and measure the voltage at each point...and it will measure 1.2v per cell, EACH TIME. i.e. will CONTINUE to show 1.2v, regardless of state of charge! So even if you wanted to, or could install some kind of meter on them-they're difficult to meter because these batteries' voltage output are pretty much all or nothing.
Anyway my questions are, if some wise person can please answer them,
-is this battery (NIMH nickel metal hydride ) an acceptable straight swap for the 7.2v, 1700 maH battery that comes with my HL King tiger,
-can i use the same charger that came with the tank or do i need another one?
-i have some familiarity with lipo batteries, when i was fooling with r/c airplanes 10 years ago. I know some people like to run their tanks a long time and they go to a lipo. But having blown up one or two lipos by charging them wrong, ( dumba$$ behavior? yes at times and not proud of it at all), I can't say i like them all that much but if they're better for some reason, i'd consider them, because i think i still have the charger around...not a minor consideration I think, really considering how it all adds up so fast.
I think the standard charge lasting a half hour or so would be fine for me, if the battery performs at the same level for a while so i don't think i will go to that kind of battery. Anyway if someone knows if this battery is worth $28 (17 pounds) i'd like to know what you think of it.
...I always lube my gearboxes ... and after My Kv... also check and make sure none of the gear axles are binding 
other recent electronics also have built in protection in it will stop the tank from driving if voltage too low.