I am getting about 6 minutes on my AXE CP too. I am beginner, so most ops are up/down and skittering across floor. Not sure if that affects the battery time or not.
I bought 2nd stock NiMH battery. Same times.
The first one lasted about 8 cycles, then died. One day, after normal charging until the charge light went out, it just didn't have enough power to get the machine off the ground. Tried charging again. Charge light was on about and hour, then went out. Same thing - no power.
I went to hobby shop and had the option of buying more of the same batteries for about $25 each or a LiPo for $65. The LiPo is a 3 cell 1350 mAH (the stock NiCD is 650 mAH). It's 11.1 Volts, the stock in 10.8 volts. I believe this is close enought to not be a problem. I got an 'Aplus' brand AP1350-20C 35 LiPo battery for $65.
It needs a LiPo charger (NEVER try to charge a LiPo battery with a charger for NiCd or NiMh batteries unless you want some fire extinguisher practice). That's about $65 - $120 for an aftermarket one that balanced the batteries (important).
The guy at the hobby shop said that the charger for the E-flite Blade CP Pro will work to charge it, but he was out of stock.
I also have a Blade CX2 which has a LiPo battery in it, but smaller and only 2 cell. Lo and behold, it's charger (EFLC3110) has 2 ports in it - one that charges the little 7.4 volt 2-cell battery in the Blade CX2, and one for charging an ll.1 Volt 3-cell. My new LiPo batter plugs right in!. Hooray!
If you don't have a Blade CX2 helicopter and its respective charger, the charger is only $22. You will need a 12V power supply though. The charger has leads to clip onto a 12V battery, but you can also get the E-flite stock AC to 12VDC power adapter (EFLC4000) that plugs right into the charger. It's about $20.
Next challenge: The connector. The aftermarket battery comes with just plain wires for the power output (a connector for the charging wires). I de-soldered the connector off the stock AXE CP battery and soldered it onto the new one. Careful! Even a new LiPo battery is charged from factory - touching the wires together will short it out and can be dangerous! Remember to put heat-shrink on the wires (before you solder the ends!) or similar electrical tape treatment.
The LiPo weighs close to the same, but it sticks out the front a lot more, resulting in a SLIGHT change of balance nose-heavy. I'll try flying it first before I decide if it needs weights added on the tail.
SUMMARY: There's a great power solution for AXE CP owners out there. You'll get about 15 minutes of flight time on the LiPo and a bit more power with no weight penalty. Get an aftermarket 1350 mAH 11.1V LiPo battery ($65), an E-flite EFLC3110 charger ($22) and an E-flite or similar AC to 12VDC power adapter ($20). Total: $107, and each of these 3 items can be used for different purposes too.
Or you can just buy about 4 stock NiMH batteries for the AXE CP for a total of about 24 minutes flight time for the same price.