Sorry if i missed this little bit of advice given in one of the other posts OR if you have already tried this but... I use KGO batts and have had this same exact problem. I will have a fully charged battery and when I go to put a carto on it, it either A - doesnt fire at all or B - gives me a low battery indication. I have found the problem isnt the battery but the carto. It's odd because if you try to mix and match 2 cartos and both your
batteries, the problem SEEMS to follow the battery and not the carto, but trust me, its the carto. What I have found is if you pull up the center pin on the carto just a touch, or even wiggle it just a touch to change the position of it, PROBLEM SOLVED! Hope this is what's going on with yours and this fixes your problem. Report back to let me know if that works out for ya or if I am a complete idiot who didn't read the full
thread well enough. LOL