From what I've heard and experienced, NIMH batteries don't last that long and their shelf life is pretty poor too. Although they are cheap and readily available... but don't be fooled, any battery can start a fire if misused, use them right and they will be fine.

my main concern is i can't take batteries out to charge,robot (security bot)will be in house where no one is

I don't plan on taking my batteries out to charge either. I'm connecting the balance lead to the balance charger, mounting both in the robot and then will make a cable to run from the balance chargers 12v barrel jack up to the barrel jack on the back of the robots body where I'll plug in the 12v supply (or have the robot do this itself eventually).

I'm tempted to fit a lipo charging bag inside too for security but from what I can gather it's only paranoid people posting about dangers of lipos and only dangerous if not used right.

I had the same thought about using that barrel jack. I don't foresee modding for self charge until I get back to the states so that's what I will do as well.

@RichMR2 that is what i was thinking but cant find any lipo chargers that will start charging right after you plug power to them. Everyone i see you have to press buttons on display to start charging. Or am i wrong?

I got myself a Turnigy 2s/3s which has no buttons, just a 12v barrel jack, a 2s balance port and a 3s balance port and two LEDs (red & green). It come from ebay with a low voltage warning board for dirt cheap.

http://www.hobbyking.com/hobbyking/store/__7637__Turnigy_balancer_Charger_2S_3S.html

That was just the top one on google from a search, look harder and you'll probably get it cheaper.

thanks that is perfect because i will have 3 battery packs 1-motor 2-ez 3-ip camera

Why not power them all from the same source? That's what I do for the EZB and motors in my build (and soon to power 6v to to servos direct from battery too). You can link more than 1 pack together in parallel to make it bigger (as in more power, 2 x 5000mAh lipos in parallel make 10000mAh) and then you wont end up with one pack being drained faster than the other two.

That is provided all 3 items can handle the voltage, I've had to fit a lipo 5a 6v regulator for the servo circuit but motors can handle 7.4v (so far at least no problems) and so can the ezb.

According to hobby king these chargers only use 800mA so you can power 4 or 5 of them from a 12V 5A supply and charge 5 batteries at once.

How safe all that is I have no idea, it is next on my to-do list to look in to all of that but am waiting on a few things to arrive for the build before I get hands on again (have other work that needs doing to pay for the robot habit)

My robot is based on a rc rock crawler so it can climb up/down stairs and motors take lot of power, ip camera(foscam)power hungry and ez not so much(as long as servos are not powered off it). Ez monitors all voltage,gas, room temp and thinking of putting temp on batteries(to be safe) so if motor/camera batteries dies before making it back to charger i can still monitor what is going on till i get home and put on charging dock