I have a 6V supply not 12V. If a resistor fails on the divider it open circuits so would give Vo 0v.

Good idea or not, I will be charging with the robot on, so charging with a load. It wont cause problems with the battery, practically everything I own that's rechargable is charged while on. I've seen many examples of batteries being charged with a load and no reported issues. I'll be taking that risk.

ok but just some good advice about how most charging systems work,the have a current circuit (sense resistor) and is senses the load so battery has some load and your system as another load it wont charge it right,now it wont hurt the battery or your design is having the charger on ,only it takes longer time charging ,like having 2 resistors in parallel or 2 batteries in parallel

I thought you are using a 12 volt battery ,6 VOLT should be fine without a zener but you said if a resistor fails thats not really true ,bottom leg of the resistor going to ground opens you get full voltage into the ADC On your 6 volt circuit if your battery fails it gets a full 6 volts ,i am thinking wont hurt it

Second item i dont know if you are using a itx board ,when when you hook up a battery to be charged. it does sometimes causes it to reset,and if only using the EZB IT MAY CAUSE IT TO RESET.

So i would first test it disconnect a charger and then reconnect it,and see if anything resets that the other reson to have another battery there are other ways too,like a special cap on the relay contacts another i think its called a azorbing cap or diode.been awhile since i ever used one ,forgot the full name it fixes spikes

i see you said you are using a 6 volt battery to power your EZB not great idea I heard DJ said that 7.4 battery is needed here is the reason regulator is a 5 volt regulator and there is a voltage drop i think its .4V since he change to a LDO (LOW DROP REGULATOR) it might be more ,without looking at the data sheet ,that meens only have about .6 volt left over plus drop out voltage is 5.2 volts on the battery

here is how to work out drop out voltage on a battery before it needs to be charged its .2 volts per cell so 6 volt has 4 cells and drop out .8 and on 7.4 volt rc battery its 5 cells at .10 volts drop out

6V works fine provided my connection issues are bluetooth related, it's something I need to test and using a 7.4 LiPo isn't entirely out of the question yet (battery type & size is something I will be looking in to over the Christmas break)

7.4 is more stable if you have a big load on the EZB, as my hbridge uses a direct battery connection for power to the 2 DC motors all the EZB is powering are 4 or 6 standard servos (depending on how I get on with the elbow servos or if I reuse the original plastic linkage.

No ITX boards are being used. ARC will run in the background on one of the pcs around my house, most probably the HTPC as that's currently where it is and has shown no issues so far. If it does then it'll be on the automation pc which is far too overpowered for it's purpose.

There isn't a lot of space in the robot to fit spare batteries or back up batteries which is why I'm not going to bother with having a change over switch for when charging etc. On future projects that'll probably change though but this one is just a basic project without too much being put in to the finer points.

Ok then that makes good sense now LIPO is one of the best batteries for robots ,since i use them sometimes it saves on weight,but some drawbacks

On the charging design it is different it CC (constant current) and CV (constant voltage) on most other chargers only need CV

But still if you do the math for a 6 volt battery and LDO thats used in EZB 6 volts - .4 volt drop out thats 5.6 your battery will work down too,before the board has issues ,like 5.5 volts you will see the regulator wont be regulating. and low battery is 5.2 volts so only .2 volts of your battery will you design work to till battery goes dead.