lerameur, If your current is not exceeding more than 2.5 amps I have to ask, What gage wire are you using to supply the motor drive electronics from the battery? You could see spikes in the current if your drive electronics have crossover problems with the H switch or if you are driving a low resistance load. This is why you should have the drive electronics wired as a separate set of feeds to the battery. What type of battery and size are you using for the drive electronics and what kind and size are you using for the microprocessor electronics? I have in the past build robotic drive systems that run off of a single 12 volt battery driving the controller electronics and dual H bridge drive electronics that can supply upto 100 amps. The only thing I had to do is to place a LC network in series with the microprocessor supply to kill some of the noise as I was using the A/D convertor on board the processor with a gyro rate sensor. The battery I used was an 18 amphour 12 volt used for UPS supply's.

Dave Purola,
N8NTA