You guys expect too much out of these pen lasers.
They are not designed for long duty cycles. And the reason they are expensive is because miniaturization while maintaining efficiency is always expensive.
Expecting labby performance from a pen size laser is expecting too much.
And maybe your batteries are no good, because in all the CNI pens I've owned, the battery life has been very good with a good set of NiMH rechargeables. I would say about 50 minutes of total use at full power.
By the way, the higher power models are not "the same" as the 5mW pens. I'm not sure what you mean by that.
The higher power models of the AAA GLPs use a >500mW pump (likely 1W because I have gotten 700mW out of one without breaking a sweat) and the drivers are almost perfect as far as regulation goes.
The fatter pens likely use the same components only with a larger host for better heat-sinking.
I've always been under the impression that if CNI is good at one thing, it's producing very high quality DPSS green pens.