Hi.
i have a Traxxas Rustler with a Velineon 3S esc. I have a non Traxxas lipo battery (Gens 5000mah) which means I have a Deans to Traxxas connector. I seem to be getting connection problems with the power to the motor cutting out when I apply the throttle and also both green and red lights intermittently flashing on the esc. I think the battery is fine. Could it be issues with the battery connection or does it sound like the battery has had it?
Thanks.

How old is the battery?
Does this problem occur right away after a fresh charge or after several minutes of use?
How old is the Deans connector?
I have found that Deans connectors tend to wear the fastest of any modern connector I have used, sometimes they wear in as fast as 6 months of use. I prefer using in line slotted bullets which can be spread with a phillips screwdriver to rejuvenate a weak connection where I have bullets that are several years old. I also shorten the leads so it's impossible to accidentally reverse the polarity

Regardless, I would encourage you to eliminate any adapters and either solder a fresh TRX plug on the battery or switch to a different bullet style plug like EC3 or in-line bullet, etc..

Once you eliminate any connection issues, then you can decide if the pack has aged.

Another thing to consider is investing in a charger which reads the IR of the battery, where anything above 7mΩ would have me questioning the integrity of the pack, more info here:
Which charger is the best?

I’ll give that a try.
Your advice is much appreciated.

Shake the car. Does it act up? If not then its a probably a capacity thing (VIR)